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 $63.71   8.130%   $68.8896   $68.89   $68.90   $68.90  
  Purchase #2 $178.33   3.854%   $185.2028   $185.20   $185.20   $185.20  
  Purchase #3 $247.97   7.277%   $266.0148   $266.01   $266.00   $266.00  
  Purchase #4 $127.34   10.597%   $140.8342   $140.83   $140.85   $140.80  
  Purchase #5 $184.65   5.254%   $194.3515   $194.35   $194.35   $194.40  
  Purchase #6 $45.38   7.581%   $48.8203   $48.82   $48.80   $48.80  
  Purchase #7 $146.94   11.820%   $164.3083   $164.31   $164.30   $164.30  
  7 purchase totals = $994.32       $1,068.4215   $1,068.41   $1,068.40   $1,068.40