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 $236.34   11.203%   $262.8172   $262.82   $262.80   $262.80  
  Purchase #2 $57.56   8.201%   $62.2805   $62.28   $62.30   $62.30  
  Purchase #3 $216.34   11.792%   $241.8508   $241.85   $241.85   $241.90  
  Purchase #4 $25.39   5.335%   $26.7446   $26.74   $26.75   $26.70  
  Purchase #5 $150.48   5.801%   $159.2093   $159.21   $159.20   $159.20  
  Purchase #6 $70.33   4.579%   $73.5504   $73.55   $73.55   $73.60  
  Purchase #7 $216.32   7.753%   $233.0913   $233.09   $233.10   $233.10  
  7 purchase totals = $972.76       $1,059.5441   $1,059.54   $1,059.55   $1,059.60