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 $187.66   10.637%   $207.6214   $207.62   $207.60   $207.60  
  Purchase #2 $58.94   11.319%   $65.6114   $65.61   $65.60   $65.60  
  Purchase #3 $87.33   9.431%   $95.5661   $95.57   $95.55   $95.60  
  Purchase #4 $236.64   10.293%   $260.9974   $261.00   $261.00   $261.00  
  Purchase #5 $232.58   5.471%   $245.3045   $245.30   $245.30   $245.30  
  Purchase #6 $208.53   7.422%   $224.0071   $224.01   $224.00   $224.00  
  Purchase #7 $24.75   7.535%   $26.6149   $26.61   $26.60   $26.60  
  7 purchase totals = $1,036.43       $1,125.7228   $1,125.72   $1,125.65   $1,125.70