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 $219.27   9.155%   $239.3442   $239.34   $239.35   $239.30  
  Purchase #2 $43.29   6.167%   $45.9597   $45.96   $45.95   $46.00  
  Purchase #3 $26.31   11.405%   $29.3107   $29.31   $29.30   $29.30  
  Purchase #4 $39.79   12.137%   $44.6193   $44.62   $44.60   $44.60  
  Purchase #5 $94.43   7.134%   $101.1666   $101.17   $101.15   $101.20  
  Purchase #6 $233.89   6.654%   $249.453   $249.45   $249.45   $249.50  
  Purchase #7 $209.53   13.489%   $237.7935   $237.79   $237.80   $237.80  
  7 purchase totals = $866.51       $947.6470   $947.64   $947.60   $947.70