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 $194.53   4.658%   $203.5912   $203.59   $203.60   $203.60  
  Purchase #2 $156.97   6.286%   $166.8371   $166.84   $166.85   $166.80  
  Purchase #3 $176.82   12.691%   $199.2602   $199.26   $199.25   $199.30  
  Purchase #4 $115.27   3.175%   $118.9298   $118.93   $118.95   $118.90  
  Purchase #5 $220.82   7.243%   $236.814   $236.81   $236.80   $236.80  
  Purchase #6 $100.53   9.456%   $110.0361   $110.04   $110.05   $110.00  
  Purchase #7 $209.97   4.762%   $219.9688   $219.97   $219.95   $220.00  
  7 purchase totals = $1,174.91       $1,255.4372   $1,255.44   $1,255.45   $1,255.40