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 $190.46   7.481%   $204.7083   $204.71   $204.70   $204.70  
  Purchase #2 $31.86   11.247%   $35.4433   $35.44   $35.45   $35.40  
  Purchase #3 $220.66   12.158%   $247.4878   $247.49   $247.50   $247.50  
  Purchase #4 $216.51   12.756%   $244.128   $244.13   $244.15   $244.10  
  Purchase #5 $21.80   4.321%   $22.742   $22.74   $22.75   $22.70  
  Purchase #6 $178.52   10.546%   $197.3467   $197.35   $197.35   $197.30  
  Purchase #7 $154.34   5.289%   $162.503   $162.50   $162.50   $162.50  
  7 purchase totals = $1,014.15       $1,114.3591   $1,114.36   $1,114.40   $1,114.20