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 $165.31   11.674%   $184.6083   $184.61   $184.60   $184.60  
  Purchase #2 $120.48   13.636%   $136.9087   $136.91   $136.90   $136.90  
  Purchase #3 $166.52   12.616%   $187.5282   $187.53   $187.55   $187.50  
  Purchase #4 $182.56   8.333%   $197.7727   $197.77   $197.75   $197.80  
  Purchase #5 $62.57   13.418%   $70.9656   $70.97   $70.95   $71.00  
  Purchase #6 $197.44   13.427%   $223.9503   $223.95   $223.95   $224.00  
  Purchase #7 $44.57   5.116%   $46.8502   $46.85   $46.85   $46.90  
  7 purchase totals = $939.45       $1,048.5840   $1,048.59   $1,048.55   $1,048.70