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 $197.57   12.771%   $222.8017   $222.80   $222.80   $222.80  
  Purchase #2 $239.92   12.817%   $270.6705   $270.67   $270.65   $270.70  
  Purchase #3 $88.44   7.637%   $95.1942   $95.19   $95.20   $95.20  
  Purchase #4 $177.34   12.202%   $198.979   $198.98   $199.00   $199.00  
  Purchase #5 $11.29   9.394%   $12.3506   $12.35   $12.35   $12.40  
  Purchase #6 $207.58   11.771%   $232.0142   $232.01   $232.00   $232.00  
  Purchase #7 $147.38   9.531%   $161.4268   $161.43   $161.45   $161.40  
  7 purchase totals = $1,069.52       $1,193.4370   $1,193.43   $1,193.45   $1,193.50