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 $178.79   11.285%   $198.9665   $198.97   $198.95   $199.00  
  Purchase #2 $101.82   5.779%   $107.7042   $107.70   $107.70   $107.70  
  Purchase #3 $95.68   7.533%   $102.8876   $102.89   $102.90   $102.90  
  Purchase #4 $243.47   10.261%   $268.4525   $268.45   $268.45   $268.50  
  Purchase #5 $145.75   9.175%   $159.1226   $159.12   $159.10   $159.10  
  Purchase #6 $50.45   10.664%   $55.83   $55.83   $55.85   $55.80  
  Purchase #7 $126.59   9.870%   $139.0844   $139.08   $139.10   $139.10  
  7 purchase totals = $942.55       $1,032.0478   $1,032.04   $1,032.05   $1,032.10