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 $141.92   3.716%   $147.1937   $147.19   $147.20   $147.20  
  Purchase #2 $194.98   11.164%   $216.7476   $216.75   $216.75   $216.70  
  Purchase #3 $151.97   7.723%   $163.7066   $163.71   $163.70   $163.70  
  Purchase #4 $47.65   4.656%   $49.8686   $49.87   $49.85   $49.90  
  Purchase #5 $148.57   5.238%   $156.3521   $156.35   $156.35   $156.40  
  Purchase #6 $113.49   6.279%   $120.616   $120.62   $120.60   $120.60  
  Purchase #7 $92.63   5.118%   $97.3708   $97.37   $97.35   $97.40  
  7 purchase totals = $891.21       $951.8554   $951.86   $951.80   $951.90