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 $194.51   11.534%   $216.9448   $216.94   $216.95   $216.90  
  Purchase #2 $235.47   4.799%   $246.7702   $246.77   $246.75   $246.80  
  Purchase #3 $88.43   6.289%   $93.9914   $93.99   $94.00   $94.00  
  Purchase #4 $71.37   8.474%   $77.4179   $77.42   $77.40   $77.40  
  Purchase #5 $101.66   13.560%   $115.4451   $115.45   $115.45   $115.40  
  Purchase #6 $233.77   11.619%   $260.9317   $260.93   $260.95   $260.90  
  Purchase #7 $50.70   6.121%   $53.8033   $53.80   $53.80   $53.80  
  7 purchase totals = $975.91       $1,065.3044   $1,065.30   $1,065.30   $1,065.20