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 $166.85   12.392%   $187.5261   $187.53   $187.55   $187.50  
  Purchase #2 $177.36   11.326%   $197.4478   $197.45   $197.45   $197.40  
  Purchase #3 $160.49   5.601%   $169.479   $169.48   $169.50   $169.50  
  Purchase #4 $70.65   4.227%   $73.6364   $73.64   $73.65   $73.60  
  Purchase #5 $234.67   11.172%   $260.8873   $260.89   $260.90   $260.90  
  Purchase #6 $24.46   8.291%   $26.488   $26.49   $26.50   $26.50  
  Purchase #7 $128.34   8.271%   $138.955   $138.96   $138.95   $139.00  
  7 purchase totals = $962.82       $1,054.4196   $1,054.44   $1,054.50   $1,054.40