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 $87.79   6.442%   $93.4454   $93.45   $93.45   $93.40  
  Purchase #2 $189.90   8.439%   $205.9257   $205.93   $205.95   $205.90  
  Purchase #3 $100.85   7.452%   $108.3653   $108.37   $108.35   $108.40  
  Purchase #4 $174.77   7.800%   $188.4021   $188.40   $188.40   $188.40  
  Purchase #5 $80.51   8.460%   $87.3211   $87.32   $87.30   $87.30  
  Purchase #6 $24.97   7.775%   $26.9114   $26.91   $26.90   $26.90  
  Purchase #7 $219.42   11.352%   $244.3286   $244.33   $244.35   $244.30  
  7 purchase totals = $878.21       $954.6996   $954.71   $954.70   $954.60