Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $197.68   4.191%   $205.9648   $205.96   $205.95   $206.00  
  Purchase #2 $173.38   6.503%   $184.6549   $184.65   $184.65   $184.70  
  Purchase #3 $232.89   8.263%   $252.1337   $252.13   $252.15   $252.10  
  Purchase #4 $119.73   7.373%   $128.5577   $128.56   $128.55   $128.60  
  Purchase #5 $185.80   8.327%   $201.2716   $201.27   $201.25   $201.30  
  Purchase #6 $155.88   9.306%   $170.3862   $170.39   $170.40   $170.40  
  Purchase #7 $130.91   10.767%   $145.0051   $145.01   $145.00   $145.00  
  7 purchase totals = $1,196.27       $1,287.9740   $1,287.97   $1,287.95   $1,288.10