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 $95.52   3.219%   $98.5948   $98.59   $98.60   $98.60  
  Purchase #2 $183.57   8.404%   $198.9972   $199.00   $199.00   $199.00  
  Purchase #3 $95.49   11.385%   $106.3615   $106.36   $106.35   $106.40  
  Purchase #4 $129.93   6.843%   $138.8211   $138.82   $138.80   $138.80  
  Purchase #5 $178.69   5.405%   $188.3482   $188.35   $188.35   $188.30  
  Purchase #6 $174.58   11.796%   $195.1735   $195.17   $195.15   $195.20  
  Purchase #7 $83.66   3.670%   $86.7303   $86.73   $86.75   $86.70  
  7 purchase totals = $941.44       $1,013.0266   $1,013.02   $1,013.00   $1,013.00