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 $68.53   6.752%   $73.1571   $73.16   $73.15   $73.20  
  Purchase #2 $142.68   3.658%   $147.8992   $147.90   $147.90   $147.90  
  Purchase #3 $243.55   13.251%   $275.8228   $275.82   $275.80   $275.80  
  Purchase #4 $22.74   11.603%   $25.3785   $25.38   $25.40   $25.40  
  Purchase #5 $46.98   5.175%   $49.4112   $49.41   $49.40   $49.40  
  Purchase #6 $30.31   8.527%   $32.8945   $32.89   $32.90   $32.90  
  Purchase #7 $221.83   7.492%   $238.4495   $238.45   $238.45   $238.40  
  7 purchase totals = $776.62       $843.0128   $843.01   $843.00   $843.00