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 $186.93   7.870%   $201.6414   $201.64   $201.65   $201.60  
  Purchase #2 $209.75   6.797%   $224.0067   $224.01   $224.00   $224.00  
  Purchase #3 $244.81   12.333%   $275.0024   $275.00   $275.00   $275.00  
  Purchase #4 $54.99   13.621%   $62.4802   $62.48   $62.50   $62.50  
  Purchase #5 $225.75   13.581%   $256.4091   $256.41   $256.40   $256.40  
  Purchase #6 $36.36   4.162%   $37.8733   $37.87   $37.85   $37.90  
  Purchase #7 $193.29   8.587%   $209.8878   $209.89   $209.90   $209.90  
  7 purchase totals = $1,151.88       $1,267.3009   $1,267.30   $1,267.30   $1,267.30