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 $57.41   9.778%   $63.0235   $63.02   $63.00   $63.00  
  Purchase #2 $126.51   6.319%   $134.5042   $134.50   $134.50   $134.50  
  Purchase #3 $94.73   6.370%   $100.7643   $100.76   $100.75   $100.80  
  Purchase #4 $211.31   6.557%   $225.1656   $225.17   $225.15   $225.20  
  Purchase #5 $214.54   12.695%   $241.7759   $241.78   $241.80   $241.80  
  Purchase #6 $86.94   8.234%   $94.0986   $94.10   $94.10   $94.10  
  Purchase #7 $138.75   5.279%   $146.0746   $146.07   $146.05   $146.10  
  7 purchase totals = $930.19       $1,005.4067   $1,005.40   $1,005.35   $1,005.50