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 $232.84   10.680%   $257.7073   $257.71   $257.70   $257.70  
  Purchase #2 $202.69   13.400%   $229.8505   $229.85   $229.85   $229.90  
  Purchase #3 $5.35   9.134%   $5.8387   $5.84   $5.85   $5.80  
  Purchase #4 $32.36   12.276%   $36.3325   $36.33   $36.35   $36.30  
  Purchase #5 $195.43   12.520%   $219.8978   $219.90   $219.90   $219.90  
  Purchase #6 $197.54   3.813%   $205.0722   $205.07   $205.05   $205.10  
  Purchase #7 $97.45   9.170%   $106.3862   $106.39   $106.40   $106.40  
  7 purchase totals = $963.66       $1,061.0852   $1,061.09   $1,061.10   $1,061.10