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 $238.79   13.714%   $271.5377   $271.54   $271.55   $271.50  
  Purchase #2 $219.48   10.136%   $241.7265   $241.73   $241.75   $241.70  
  Purchase #3 $58.37   13.692%   $66.362   $66.36   $66.35   $66.40  
  Purchase #4 $224.95   7.148%   $241.0294   $241.03   $241.05   $241.00  
  Purchase #5 $24.72   7.693%   $26.6217   $26.62   $26.60   $26.60  
  Purchase #6 $159.79   10.631%   $176.7773   $176.78   $176.80   $176.80  
  Purchase #7 $217.59   6.368%   $231.4461   $231.45   $231.45   $231.40  
  7 purchase totals = $1,143.69       $1,255.5007   $1,255.51   $1,255.55   $1,255.40