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 $202.27   11.607%   $225.7475   $225.75   $225.75   $225.70  
  Purchase #2 $238.35   13.800%   $271.2423   $271.24   $271.25   $271.20  
  Purchase #3 $11.29   6.290%   $12.0001   $12.00   $12.00   $12.00  
  Purchase #4 $98.25   13.858%   $111.8655   $111.87   $111.85   $111.90  
  Purchase #5 $236.53   4.132%   $246.3034   $246.30   $246.30   $246.30  
  Purchase #6 $79.60   6.386%   $84.6833   $84.68   $84.70   $84.70  
  Purchase #7 $228.54   6.312%   $242.9654   $242.97   $242.95   $243.00  
  7 purchase totals = $1,094.83       $1,194.8075   $1,194.81   $1,194.80   $1,194.80