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 $229.82   13.454%   $260.74   $260.74   $260.75   $260.70  
  Purchase #2 $205.88   11.864%   $230.3056   $230.31   $230.30   $230.30  
  Purchase #3 $197.43   6.870%   $210.9934   $210.99   $211.00   $211.00  
  Purchase #4 $37.25   13.353%   $42.224   $42.22   $42.20   $42.20  
  Purchase #5 $20.71   10.812%   $22.9492   $22.95   $22.95   $22.90  
  Purchase #6 $149.30   3.557%   $154.6106   $154.61   $154.60   $154.60  
  Purchase #7 $247.37   11.165%   $274.9889   $274.99   $275.00   $275.00  
  7 purchase totals = $1,087.76       $1,196.8117   $1,196.81   $1,196.80   $1,196.70