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 $103.82   13.315%   $117.6436   $117.64   $117.65   $117.60  
  Purchase #2 $240.78   9.809%   $264.3981   $264.40   $264.40   $264.40  
  Purchase #3 $73.95   9.815%   $81.2082   $81.21   $81.20   $81.20  
  Purchase #4 $221.91   9.694%   $243.422   $243.42   $243.40   $243.40  
  Purchase #5 $111.59   5.385%   $117.5991   $117.60   $117.60   $117.60  
  Purchase #6 $115.52   5.333%   $121.6807   $121.68   $121.70   $121.70  
  Purchase #7 $24.41   10.801%   $27.0465   $27.05   $27.05   $27.00  
  7 purchase totals = $891.98       $972.9982   $973.00   $973.00   $972.90