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 $39.66   11.774%   $44.3296   $44.33   $44.35   $44.30  
  Purchase #2 $189.92   8.349%   $205.7764   $205.78   $205.80   $205.80  
  Purchase #3 $73.99   13.171%   $83.7352   $83.74   $83.75   $83.70  
  Purchase #4 $229.95   4.873%   $241.1555   $241.16   $241.15   $241.20  
  Purchase #5 $195.46   4.627%   $204.5039   $204.50   $204.50   $204.50  
  Purchase #6 $87.74   11.202%   $97.5686   $97.57   $97.55   $97.60  
  Purchase #7 $171.43   10.305%   $189.0959   $189.10   $189.10   $189.10  
  7 purchase totals = $988.15       $1,066.1651   $1,066.18   $1,066.20   $1,066.20