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 $58.76   8.704%   $63.8745   $63.87   $63.85   $63.90  
  Purchase #2 $116.30   10.154%   $128.1091   $128.11   $128.10   $128.10  
  Purchase #3 $146.36   3.860%   $152.0095   $152.01   $152.00   $152.00  
  Purchase #4 $64.28   7.209%   $68.9139   $68.91   $68.90   $68.90  
  Purchase #5 $71.26   5.813%   $75.4023   $75.40   $75.40   $75.40  
  Purchase #6 $213.42   11.816%   $238.6377   $238.64   $238.65   $238.60  
  Purchase #7 $193.35   9.644%   $211.9967   $212.00   $212.00   $212.00  
  7 purchase totals = $863.73       $938.9437   $938.94   $938.90   $938.90