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 $41.52   11.812%   $46.4243   $46.42   $46.40   $46.40  
  Purchase #2 $174.79   8.419%   $189.5056   $189.51   $189.50   $189.50  
  Purchase #3 $217.89   3.212%   $224.8886   $224.89   $224.90   $224.90  
  Purchase #4 $68.45   7.592%   $73.6467   $73.65   $73.65   $73.60  
  Purchase #5 $142.89   3.612%   $148.0512   $148.05   $148.05   $148.10  
  Purchase #6 $179.44   3.677%   $186.038   $186.04   $186.05   $186.00  
  Purchase #7 $82.99   5.376%   $87.4515   $87.45   $87.45   $87.50  
  7 purchase totals = $907.97       $956.0059   $956.01   $956.00   $956.00