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 $13.65   8.252%   $14.7764   $14.78   $14.80   $14.80  
  Purchase #2 $48.56   8.439%   $52.658   $52.66   $52.65   $52.70  
  Purchase #3 $195.49   11.261%   $217.5041   $217.50   $217.50   $217.50  
  Purchase #4 $173.79   13.201%   $196.732   $196.73   $196.75   $196.70  
  Purchase #5 $184.73   10.824%   $204.7252   $204.73   $204.75   $204.70  
  Purchase #6 $245.55   9.107%   $267.9122   $267.91   $267.90   $267.90  
  Purchase #7 $157.30   8.340%   $170.4188   $170.42   $170.40   $170.40  
  7 purchase totals = $1,019.07       $1,124.7267   $1,124.73   $1,124.75   $1,124.70