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 $119.65   11.699%   $133.6479   $133.65   $133.65   $133.60  
  Purchase #2 $106.94   5.786%   $113.1275   $113.13   $113.15   $113.10  
  Purchase #3 $12.29   5.451%   $12.9599   $12.96   $12.95   $13.00  
  Purchase #4 $46.87   8.209%   $50.7176   $50.72   $50.70   $50.70  
  Purchase #5 $245.58   7.506%   $264.0132   $264.01   $264.00   $264.00  
  Purchase #6 $61.36   3.448%   $63.4757   $63.48   $63.50   $63.50  
  Purchase #7 $113.49   5.246%   $119.4437   $119.44   $119.45   $119.40  
  7 purchase totals = $706.18       $757.3855   $757.39   $757.40   $757.30