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 $89.34   10.207%   $98.4589   $98.46   $98.45   $98.50  
  Purchase #2 $204.33   9.754%   $224.2603   $224.26   $224.25   $224.30  
  Purchase #3 $112.75   9.680%   $123.6642   $123.66   $123.65   $123.70  
  Purchase #4 $240.73   5.653%   $254.3385   $254.34   $254.35   $254.30  
  Purchase #5 $106.35   8.567%   $115.461   $115.46   $115.45   $115.50  
  Purchase #6 $226.33   9.473%   $247.7702   $247.77   $247.75   $247.80  
  Purchase #7 $51.41   13.326%   $58.2609   $58.26   $58.25   $58.30  
  7 purchase totals = $1,031.24       $1,122.2140   $1,122.21   $1,122.15   $1,122.40