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 $79.61   8.713%   $86.5464   $86.55   $86.55   $86.50  
  Purchase #2 $213.85   4.769%   $224.0485   $224.05   $224.05   $224.00  
  Purchase #3 $163.33   9.604%   $179.0162   $179.02   $179.00   $179.00  
  Purchase #4 $199.37   4.253%   $207.8492   $207.85   $207.85   $207.80  
  Purchase #5 $98.72   7.150%   $105.7785   $105.78   $105.80   $105.80  
  Purchase #6 $250.52   9.814%   $275.106   $275.11   $275.10   $275.10  
  Purchase #7 $88.81   4.862%   $93.1279   $93.13   $93.15   $93.10  
  7 purchase totals = $1,094.21       $1,171.4727   $1,171.49   $1,171.50   $1,171.30