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 $67.47   13.133%   $76.3308   $76.33   $76.35   $76.30  
  Purchase #2 $212.84   12.408%   $239.2492   $239.25   $239.25   $239.20  
  Purchase #3 $110.69   8.778%   $120.4064   $120.41   $120.40   $120.40  
  Purchase #4 $87.38   9.381%   $95.5771   $95.58   $95.60   $95.60  
  Purchase #5 $42.32   6.641%   $45.1305   $45.13   $45.15   $45.10  
  Purchase #6 $223.91   10.453%   $247.3153   $247.32   $247.30   $247.30  
  Purchase #7 $64.76   8.811%   $70.466   $70.47   $70.45   $70.50  
  7 purchase totals = $809.37       $894.4753   $894.49   $894.50   $894.40