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 $204.82   13.435%   $232.3376   $232.34   $232.35   $232.30  
  Purchase #2 $108.72   12.451%   $122.2567   $122.26   $122.25   $122.30  
  Purchase #3 $137.31   6.268%   $145.9166   $145.92   $145.90   $145.90  
  Purchase #4 $197.94   4.573%   $206.9918   $206.99   $207.00   $207.00  
  Purchase #5 $187.38   5.154%   $197.0376   $197.04   $197.05   $197.00  
  Purchase #6 $122.33   8.602%   $132.8528   $132.85   $132.85   $132.90  
  Purchase #7 $214.26   5.219%   $225.4422   $225.44   $225.45   $225.40  
  7 purchase totals = $1,172.76       $1,262.8353   $1,262.84   $1,262.85   $1,262.80