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 $43.79   5.859%   $46.3557   $46.36   $46.35   $46.40  
  Purchase #2 $235.75   3.484%   $243.9635   $243.96   $243.95   $244.00  
  Purchase #3 $50.85   4.789%   $53.2852   $53.29   $53.30   $53.30  
  Purchase #4 $211.70   7.808%   $228.2295   $228.23   $228.25   $228.20  
  Purchase #5 $240.64   9.865%   $264.3791   $264.38   $264.40   $264.40  
  Purchase #6 $62.79   10.574%   $69.4294   $69.43   $69.45   $69.40  
  Purchase #7 $105.65   10.789%   $117.0486   $117.05   $117.05   $117.00  
  7 purchase totals = $951.17       $1,022.6910   $1,022.70   $1,022.75   $1,022.70