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 $236.27   3.593%   $244.7592   $244.76   $244.75   $244.80  
  Purchase #2 $18.56   6.113%   $19.6946   $19.69   $19.70   $19.70  
  Purchase #3 $131.52   11.669%   $146.8671   $146.87   $146.85   $146.90  
  Purchase #4 $236.26   10.185%   $260.3231   $260.32   $260.30   $260.30  
  Purchase #5 $160.78   10.288%   $177.321   $177.32   $177.30   $177.30  
  Purchase #6 $143.45   4.760%   $150.2782   $150.28   $150.30   $150.30  
  Purchase #7 $80.82   13.812%   $91.9829   $91.98   $92.00   $92.00  
  7 purchase totals = $1,007.66       $1,091.2261   $1,091.22   $1,091.20   $1,091.30