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 $191.50   11.851%   $214.1947   $214.19   $214.20   $214.20  
  Purchase #2 $138.33   8.828%   $150.5418   $150.54   $150.55   $150.50  
  Purchase #3 $189.29   6.153%   $200.937   $200.94   $200.95   $200.90  
  Purchase #4 $25.53   3.118%   $26.326   $26.33   $26.35   $26.30  
  Purchase #5 $201.39   11.313%   $224.1733   $224.17   $224.15   $224.20  
  Purchase #6 $223.62   11.761%   $249.9199   $249.92   $249.90   $249.90  
  Purchase #7 $33.62   5.705%   $35.538   $35.54   $35.55   $35.50  
  7 purchase totals = $1,003.28       $1,101.6307   $1,101.63   $1,101.65   $1,101.50