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 $92.58   4.231%   $96.4971   $96.50   $96.50   $96.50  
  Purchase #2 $187.39   9.515%   $205.2202   $205.22   $205.20   $205.20  
  Purchase #3 $23.41   8.787%   $25.467   $25.47   $25.45   $25.50  
  Purchase #4 $48.58   13.379%   $55.0795   $55.08   $55.10   $55.10  
  Purchase #5 $197.78   9.350%   $216.2724   $216.27   $216.25   $216.30  
  Purchase #6 $30.94   10.549%   $34.2039   $34.20   $34.20   $34.20  
  Purchase #7 $200.48   5.562%   $211.6307   $211.63   $211.65   $211.60  
  7 purchase totals = $781.16       $844.3708   $844.37   $844.35   $844.40