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 $20.80   12.856%   $23.474   $23.47   $23.45   $23.50  
  Purchase #2 $62.51   8.787%   $68.0028   $68.00   $68.00   $68.00  
  Purchase #3 $92.52   10.698%   $102.4178   $102.42   $102.40   $102.40  
  Purchase #4 $163.55   5.352%   $172.3032   $172.30   $172.30   $172.30  
  Purchase #5 $38.84   9.611%   $42.5729   $42.57   $42.55   $42.60  
  Purchase #6 $89.30   4.350%   $93.1846   $93.18   $93.20   $93.20  
  Purchase #7 $193.67   13.818%   $220.4313   $220.43   $220.45   $220.40  
  7 purchase totals = $661.19       $722.3866   $722.37   $722.35   $722.40