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 $40.87   8.384%   $44.2965   $44.30   $44.30   $44.30  
  Purchase #2 $169.78   7.551%   $182.6001   $182.60   $182.60   $182.60  
  Purchase #3 $225.69   12.526%   $253.9599   $253.96   $253.95   $254.00  
  Purchase #4 $77.65   3.599%   $80.4446   $80.44   $80.45   $80.40  
  Purchase #5 $143.71   12.809%   $162.1178   $162.12   $162.10   $162.10  
  Purchase #6 $75.68   7.502%   $81.3575   $81.36   $81.35   $81.40  
  Purchase #7 $194.25   5.775%   $205.4679   $205.47   $205.45   $205.50  
  7 purchase totals = $927.63       $1,010.2443   $1,010.25   $1,010.20   $1,010.30