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 $219.97   11.395%   $245.0356   $245.04   $245.05   $245.00  
  Purchase #2 $67.32   13.872%   $76.6586   $76.66   $76.65   $76.70  
  Purchase #3 $237.47   8.214%   $256.9758   $256.98   $257.00   $257.00  
  Purchase #4 $192.59   8.749%   $209.4397   $209.44   $209.45   $209.40  
  Purchase #5 $52.89   10.872%   $58.6402   $58.64   $58.65   $58.60  
  Purchase #6 $215.86   4.381%   $225.3168   $225.32   $225.30   $225.30  
  Purchase #7 $181.53   11.427%   $202.2734   $202.27   $202.25   $202.30  
  7 purchase totals = $1,167.63       $1,274.3401   $1,274.35   $1,274.35   $1,274.30