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 $104.87   13.755%   $119.2949   $119.29   $119.30   $119.30  
  Purchase #2 $223.99   8.329%   $242.6461   $242.65   $242.65   $242.60  
  Purchase #3 $67.89   6.145%   $72.0618   $72.06   $72.05   $72.10  
  Purchase #4 $113.92   5.510%   $120.197   $120.20   $120.20   $120.20  
  Purchase #5 $129.66   13.360%   $146.9826   $146.98   $147.00   $147.00  
  Purchase #6 $145.90   9.241%   $159.3826   $159.38   $159.40   $159.40  
  Purchase #7 $98.87   8.138%   $106.916   $106.92   $106.90   $106.90  
  7 purchase totals = $885.10       $967.4810   $967.48   $967.50   $967.50