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 $58.47   8.713%   $63.5645   $63.56   $63.55   $63.60  
  Purchase #2 $118.55   13.453%   $134.4985   $134.50   $134.50   $134.50  
  Purchase #3 $240.25   9.126%   $262.1752   $262.18   $262.20   $262.20  
  Purchase #4 $148.66   4.360%   $155.1416   $155.14   $155.15   $155.10  
  Purchase #5 $88.59   6.536%   $94.3802   $94.38   $94.40   $94.40  
  Purchase #6 $102.95   11.858%   $115.1578   $115.16   $115.15   $115.20  
  Purchase #7 $103.87   5.608%   $109.695   $109.70   $109.70   $109.70  
  7 purchase totals = $861.34       $934.6128   $934.62   $934.65   $934.70