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 $214.63   13.276%   $243.1243   $243.12   $243.10   $243.10  
  Purchase #2 $237.37   11.792%   $265.3607   $265.36   $265.35   $265.40  
  Purchase #3 $150.99   7.851%   $162.8442   $162.84   $162.85   $162.80  
  Purchase #4 $114.46   11.266%   $127.3551   $127.36   $127.35   $127.40  
  Purchase #5 $14.65   6.606%   $15.6178   $15.62   $15.60   $15.60  
  Purchase #6 $232.29   6.413%   $247.1868   $247.19   $247.20   $247.20  
  Purchase #7 $131.79   5.261%   $138.7235   $138.72   $138.70   $138.70  
  7 purchase totals = $1,096.18       $1,200.2124   $1,200.21   $1,200.15   $1,200.20