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 $89.28   7.438%   $95.9206   $95.92   $95.90   $95.90  
  Purchase #2 $245.68   6.503%   $261.6566   $261.66   $261.65   $261.70  
  Purchase #3 $195.52   3.390%   $202.1481   $202.15   $202.15   $202.10  
  Purchase #4 $61.53   10.197%   $67.8042   $67.80   $67.80   $67.80  
  Purchase #5 $164.77   9.806%   $180.9273   $180.93   $180.95   $180.90  
  Purchase #6 $209.47   5.134%   $220.2242   $220.22   $220.20   $220.20  
  Purchase #7 $188.40   9.625%   $206.5335   $206.53   $206.55   $206.50  
  7 purchase totals = $1,154.65       $1,235.2145   $1,235.21   $1,235.20   $1,235.10