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 $49.41   6.464%   $52.6039   $52.60   $52.60   $52.60  
  Purchase #2 $211.97   6.832%   $226.4518   $226.45   $226.45   $226.50  
  Purchase #3 $165.61   13.280%   $187.603   $187.60   $187.60   $187.60  
  Purchase #4 $169.84   4.614%   $177.6764   $177.68   $177.70   $177.70  
  Purchase #5 $9.73   4.676%   $10.185   $10.19   $10.20   $10.20  
  Purchase #6 $218.58   12.774%   $246.5014   $246.50   $246.50   $246.50  
  Purchase #7 $12.83   12.352%   $14.4148   $14.41   $14.40   $14.40  
  7 purchase totals = $837.97       $915.4363   $915.43   $915.45   $915.50