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 $238.83   6.478%   $254.3014   $254.30   $254.30   $254.30  
  Purchase #2 $47.94   11.236%   $53.3265   $53.33   $53.35   $53.30  
  Purchase #3 $221.37   3.348%   $228.7815   $228.78   $228.80   $228.80  
  Purchase #4 $158.51   9.290%   $173.2356   $173.24   $173.25   $173.20  
  Purchase #5 $15.93   12.702%   $17.9534   $17.95   $17.95   $18.00  
  Purchase #6 $163.34   9.378%   $178.658   $178.66   $178.65   $178.70  
  Purchase #7 $43.94   9.349%   $48.048   $48.05   $48.05   $48.00  
  7 purchase totals = $889.86       $954.3044   $954.31   $954.35   $954.30