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 $101.84   7.621%   $109.6012   $109.60   $109.60   $109.60  
  Purchase #2 $225.98   13.613%   $256.7427   $256.74   $256.75   $256.70  
  Purchase #3 $36.74   11.611%   $41.0059   $41.01   $41.00   $41.00  
  Purchase #4 $65.32   6.839%   $69.7872   $69.79   $69.80   $69.80  
  Purchase #5 $225.48   11.327%   $251.0201   $251.02   $251.00   $251.00  
  Purchase #6 $124.62   5.417%   $131.3707   $131.37   $131.35   $131.40  
  Purchase #7 $169.77   11.794%   $189.7927   $189.79   $189.80   $189.80  
  7 purchase totals = $949.75       $1,049.3205   $1,049.32   $1,049.30   $1,049.30