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 $44.96   8.131%   $48.6157   $48.62   $48.60   $48.60  
  Purchase #2 $152.82   8.390%   $165.6416   $165.64   $165.65   $165.60  
  Purchase #3 $23.68   9.755%   $25.99   $25.99   $26.00   $26.00  
  Purchase #4 $11.91   9.539%   $13.0461   $13.05   $13.05   $13.00  
  Purchase #5 $31.65   5.227%   $33.3043   $33.30   $33.30   $33.30  
  Purchase #6 $66.87   8.262%   $72.3948   $72.39   $72.40   $72.40  
  Purchase #7 $42.46   3.195%   $43.8166   $43.82   $43.80   $43.80  
  7 purchase totals = $374.35       $402.8091   $402.81   $402.80   $402.70