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 $45.72   4.249%   $47.6626   $47.66   $47.65   $47.70  
  Purchase #2 $97.41   4.413%   $101.7087   $101.71   $101.70   $101.70  
  Purchase #3 $191.86   6.148%   $203.6556   $203.66   $203.65   $203.70  
  Purchase #4 $226.41   4.236%   $236.0007   $236.00   $236.00   $236.00  
  Purchase #5 $96.32   5.402%   $101.5232   $101.52   $101.50   $101.50  
  Purchase #6 $169.78   8.541%   $184.2809   $184.28   $184.30   $184.30  
  Purchase #7 $122.91   3.261%   $126.9181   $126.92   $126.90   $126.90  
  7 purchase totals = $950.41       $1,001.7498   $1,001.75   $1,001.70   $1,001.80