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 $27.73   6.850%   $29.6295   $29.63   $29.65   $29.60  
  Purchase #2 $209.83   13.473%   $238.1004   $238.10   $238.10   $238.10  
  Purchase #3 $95.83   8.543%   $104.0168   $104.02   $104.00   $104.00  
  Purchase #4 $185.63   10.820%   $205.7152   $205.72   $205.70   $205.70  
  Purchase #5 $57.42   13.557%   $65.2044   $65.20   $65.20   $65.20  
  Purchase #6 $163.96   11.130%   $182.2087   $182.21   $182.20   $182.20  
  Purchase #7 $218.56   11.418%   $243.5152   $243.52   $243.50   $243.50  
  7 purchase totals = $958.96       $1,068.3902   $1,068.40   $1,068.35   $1,068.30