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 $62.81   11.121%   $69.7951   $69.80   $69.80   $69.80  
  Purchase #2 $197.26   12.344%   $221.6098   $221.61   $221.60   $221.60  
  Purchase #3 $140.81   9.630%   $154.37   $154.37   $154.35   $154.40  
  Purchase #4 $233.51   9.597%   $255.92   $255.92   $255.90   $255.90  
  Purchase #5 $88.60   13.241%   $100.3315   $100.33   $100.35   $100.30  
  Purchase #6 $244.98   10.663%   $271.1022   $271.10   $271.10   $271.10  
  Purchase #7 $138.83   13.142%   $157.075   $157.08   $157.10   $157.10  
  7 purchase totals = $1,106.80       $1,230.2036   $1,230.21   $1,230.20   $1,230.20