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 $48.79   12.206%   $54.7453   $54.75   $54.75   $54.70  
  Purchase #2 $124.98   8.869%   $136.0645   $136.06   $136.05   $136.10  
  Purchase #3 $151.81   9.157%   $165.7112   $165.71   $165.70   $165.70  
  Purchase #4 $133.95   3.242%   $138.2927   $138.29   $138.30   $138.30  
  Purchase #5 $15.69   7.183%   $16.817   $16.82   $16.80   $16.80  
  Purchase #6 $99.87   7.677%   $107.537   $107.54   $107.55   $107.50  
  Purchase #7 $187.34   10.469%   $206.9526   $206.95   $206.95   $207.00  
  7 purchase totals = $762.43       $826.1203   $826.12   $826.10   $826.10