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 $52.99   13.731%   $60.2661   $60.27   $60.25   $60.30  
  Purchase #2 $191.38   6.835%   $204.4608   $204.46   $204.45   $204.50  
  Purchase #3 $227.51   8.698%   $247.2988   $247.30   $247.30   $247.30  
  Purchase #4 $166.91   10.822%   $184.973   $184.97   $184.95   $185.00  
  Purchase #5 $235.46   9.227%   $257.1859   $257.19   $257.20   $257.20  
  Purchase #6 $210.39   4.244%   $219.319   $219.32   $219.30   $219.30  
  Purchase #7 $249.25   7.772%   $268.6217   $268.62   $268.60   $268.60  
  7 purchase totals = $1,333.89       $1,442.1253   $1,442.13   $1,442.05   $1,442.20