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 $210.80   9.313%   $230.4318   $230.43   $230.45   $230.40  
  Purchase #2 $16.29   11.398%   $18.1467   $18.15   $18.15   $18.10  
  Purchase #3 $229.31   4.764%   $240.2343   $240.23   $240.25   $240.20  
  Purchase #4 $70.49   12.460%   $79.2731   $79.27   $79.25   $79.30  
  Purchase #5 $14.89   12.831%   $16.8005   $16.80   $16.80   $16.80  
  Purchase #6 $117.76   9.312%   $128.7258   $128.73   $128.75   $128.70  
  Purchase #7 $87.93   12.864%   $99.2413   $99.24   $99.25   $99.20  
  7 purchase totals = $747.47       $812.8535   $812.85   $812.90   $812.70