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 $220.73   12.446%   $248.2021   $248.20   $248.20   $248.20  
  Purchase #2 $219.98   12.202%   $246.822   $246.82   $246.80   $246.80  
  Purchase #3 $178.46   7.456%   $191.766   $191.77   $191.75   $191.80  
  Purchase #4 $57.28   4.365%   $59.7803   $59.78   $59.80   $59.80  
  Purchase #5 $176.47   9.395%   $193.0494   $193.05   $193.05   $193.00  
  Purchase #6 $201.26   12.687%   $226.7939   $226.79   $226.80   $226.80  
  Purchase #7 $241.43   10.831%   $267.5793   $267.58   $267.60   $267.60  
  7 purchase totals = $1,295.61       $1,433.9930   $1,433.99   $1,434.00   $1,434.00