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 $73.85   13.604%   $83.8966   $83.90   $83.90   $83.90  
  Purchase #2 $167.96   9.707%   $184.2639   $184.26   $184.25   $184.30  
  Purchase #3 $239.94   6.232%   $254.8931   $254.89   $254.90   $254.90  
  Purchase #4 $36.96   11.117%   $41.0688   $41.07   $41.05   $41.10  
  Purchase #5 $245.79   6.254%   $261.1617   $261.16   $261.15   $261.20  
  Purchase #6 $176.37   13.165%   $199.5891   $199.59   $199.60   $199.60  
  Purchase #7 $178.48   13.140%   $201.9323   $201.93   $201.95   $201.90  
  7 purchase totals = $1,119.35       $1,226.8055   $1,226.80   $1,226.80   $1,226.90