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 $232.71   4.852%   $244.0011   $244.00   $244.00   $244.00  
  Purchase #2 $174.85   8.717%   $190.0917   $190.09   $190.10   $190.10  
  Purchase #3 $141.88   12.314%   $159.3511   $159.35   $159.35   $159.40  
  Purchase #4 $23.72   7.768%   $25.5626   $25.56   $25.55   $25.60  
  Purchase #5 $99.55   13.679%   $113.1674   $113.17   $113.15   $113.20  
  Purchase #6 $140.48   8.428%   $152.3197   $152.32   $152.30   $152.30  
  Purchase #7 $118.48   8.503%   $128.5544   $128.55   $128.55   $128.60  
  7 purchase totals = $931.67       $1,013.0480   $1,013.04   $1,013.00   $1,013.20