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 $217.97   8.710%   $236.9552   $236.96   $236.95   $237.00  
  Purchase #2 $137.58   9.260%   $150.3199   $150.32   $150.30   $150.30  
  Purchase #3 $61.32   12.481%   $68.9733   $68.97   $68.95   $69.00  
  Purchase #4 $55.52   12.547%   $62.4861   $62.49   $62.50   $62.50  
  Purchase #5 $147.94   3.183%   $152.6489   $152.65   $152.65   $152.60  
  Purchase #6 $108.85   8.218%   $117.7953   $117.80   $117.80   $117.80  
  Purchase #7 $226.52   12.523%   $254.8871   $254.89   $254.90   $254.90  
  7 purchase totals = $955.70       $1,044.0658   $1,044.08   $1,044.05   $1,044.10