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 $236.35   6.715%   $252.2209   $252.22   $252.20   $252.20  
  Purchase #2 $60.69   7.574%   $65.2867   $65.29   $65.30   $65.30  
  Purchase #3 $232.53   3.148%   $239.85   $239.85   $239.85   $239.90  
  Purchase #4 $69.91   8.428%   $75.802   $75.80   $75.80   $75.80  
  Purchase #5 $209.72   4.149%   $218.4213   $218.42   $218.40   $218.40  
  Purchase #6 $50.58   4.802%   $53.0089   $53.01   $53.00   $53.00  
  Purchase #7 $53.88   7.157%   $57.7362   $57.74   $57.75   $57.70  
  7 purchase totals = $913.66       $962.3260   $962.33   $962.30   $962.30