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 $84.27   11.562%   $94.0133   $94.01   $94.00   $94.00  
  Purchase #2 $144.30   12.273%   $162.0099   $162.01   $162.00   $162.00  
  Purchase #3 $224.51   11.306%   $249.8931   $249.89   $249.90   $249.90  
  Purchase #4 $132.87   4.145%   $138.3775   $138.38   $138.40   $138.40  
  Purchase #5 $93.35   7.561%   $100.4082   $100.41   $100.40   $100.40  
  Purchase #6 $205.96   6.325%   $218.987   $218.99   $219.00   $219.00  
  Purchase #7 $250.43   7.255%   $268.5987   $268.60   $268.60   $268.60  
  7 purchase totals = $1,135.69       $1,232.2877   $1,232.29   $1,232.30   $1,232.30