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 $211.55   10.123%   $232.9652   $232.97   $232.95   $233.00  
  Purchase #2 $75.53   11.618%   $84.3051   $84.31   $84.30   $84.30  
  Purchase #3 $244.47   11.755%   $273.2074   $273.21   $273.20   $273.20  
  Purchase #4 $48.29   6.758%   $51.5534   $51.55   $51.55   $51.60  
  Purchase #5 $63.49   9.493%   $69.5171   $69.52   $69.50   $69.50  
  Purchase #6 $129.73   4.764%   $135.9103   $135.91   $135.90   $135.90  
  Purchase #7 $100.42   11.484%   $111.9522   $111.95   $111.95   $112.00  
  7 purchase totals = $873.48       $959.4107   $959.42   $959.35   $959.50