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 $209.59   12.653%   $236.1094   $236.11   $236.10   $236.10  
  Purchase #2 $215.48   7.818%   $232.3262   $232.33   $232.35   $232.30  
  Purchase #3 $223.37   9.839%   $245.3474   $245.35   $245.35   $245.30  
  Purchase #4 $129.38   13.727%   $147.14   $147.14   $147.15   $147.10  
  Purchase #5 $200.69   12.428%   $225.6318   $225.63   $225.65   $225.60  
  Purchase #6 $243.88   10.273%   $268.9338   $268.93   $268.95   $268.90  
  Purchase #7 $56.86   4.593%   $59.4716   $59.47   $59.45   $59.50  
  7 purchase totals = $1,279.25       $1,414.9602   $1,414.96   $1,415.00   $1,414.80