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 $54.59   13.722%   $62.0808   $62.08   $62.10   $62.10  
  Purchase #2 $51.43   9.862%   $56.502   $56.50   $56.50   $56.50  
  Purchase #3 $165.71   5.615%   $175.0146   $175.01   $175.00   $175.00  
  Purchase #4 $128.30   4.740%   $134.3814   $134.38   $134.40   $134.40  
  Purchase #5 $195.65   8.252%   $211.795   $211.80   $211.80   $211.80  
  Purchase #6 $21.89   8.222%   $23.6898   $23.69   $23.70   $23.70  
  Purchase #7 $240.27   12.823%   $271.0798   $271.08   $271.10   $271.10  
  7 purchase totals = $857.84       $934.5434   $934.54   $934.60   $934.60