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 $41.55   11.871%   $46.4824   $46.48   $46.50   $46.50  
  Purchase #2 $217.98   12.229%   $244.6368   $244.64   $244.65   $244.60  
  Purchase #3 $166.35   12.399%   $186.9757   $186.98   $187.00   $187.00  
  Purchase #4 $144.67   9.711%   $158.7189   $158.72   $158.70   $158.70  
  Purchase #5 $107.94   10.585%   $119.3654   $119.37   $119.35   $119.40  
  Purchase #6 $106.51   8.275%   $115.3237   $115.32   $115.30   $115.30  
  Purchase #7 $35.28   12.435%   $39.6671   $39.67   $39.65   $39.70  
  7 purchase totals = $820.28       $911.1700   $911.18   $911.15   $911.20