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 $92.64   12.376%   $104.1051   $104.11   $104.10   $104.10  
  Purchase #2 $242.34   6.515%   $258.1285   $258.13   $258.15   $258.10  
  Purchase #3 $25.40   7.566%   $27.3218   $27.32   $27.30   $27.30  
  Purchase #4 $117.40   7.270%   $125.935   $125.94   $125.95   $125.90  
  Purchase #5 $75.55   11.133%   $83.961   $83.96   $83.95   $84.00  
  Purchase #6 $250.56   13.169%   $283.5562   $283.56   $283.55   $283.60  
  Purchase #7 $234.28   12.466%   $263.4853   $263.49   $263.50   $263.50  
  7 purchase totals = $1,038.17       $1,146.4929   $1,146.51   $1,146.50   $1,146.50