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 $205.88   13.792%   $234.275   $234.28   $234.30   $234.30  
  Purchase #2 $93.65   9.616%   $102.6554   $102.66   $102.65   $102.70  
  Purchase #3 $103.26   11.434%   $115.0667   $115.07   $115.05   $115.10  
  Purchase #4 $58.39   7.511%   $62.7757   $62.78   $62.80   $62.80  
  Purchase #5 $239.79   3.384%   $247.9045   $247.90   $247.90   $247.90  
  Purchase #6 $226.87   8.633%   $246.4557   $246.46   $246.45   $246.50  
  Purchase #7 $129.80   9.433%   $142.044   $142.04   $142.05   $142.00  
  7 purchase totals = $1,057.64       $1,151.1770   $1,151.19   $1,151.20   $1,151.30