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 $212.63   10.424%   $234.7946   $234.79   $234.80   $234.80  
  Purchase #2 $136.77   8.485%   $148.3749   $148.37   $148.35   $148.40  
  Purchase #3 $25.87   7.869%   $27.9057   $27.91   $27.90   $27.90  
  Purchase #4 $207.66   13.819%   $236.3565   $236.36   $236.35   $236.40  
  Purchase #5 $107.42   11.525%   $119.8002   $119.80   $119.80   $119.80  
  Purchase #6 $44.85   4.336%   $46.7947   $46.79   $46.80   $46.80  
  Purchase #7 $191.30   8.630%   $207.8092   $207.81   $207.80   $207.80  
  7 purchase totals = $926.50       $1,021.8358   $1,021.83   $1,021.80   $1,021.90