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 $52.73   6.773%   $56.3014   $56.30   $56.30   $56.30  
  Purchase #2 $185.40   8.578%   $201.3036   $201.30   $201.30   $201.30  
  Purchase #3 $34.38   13.456%   $39.0062   $39.01   $39.00   $39.00  
  Purchase #4 $246.87   11.121%   $274.3244   $274.32   $274.30   $274.30  
  Purchase #5 $67.83   12.329%   $76.1928   $76.19   $76.20   $76.20  
  Purchase #6 $244.94   6.341%   $260.4716   $260.47   $260.45   $260.50  
  Purchase #7 $197.47   7.307%   $211.8991   $211.90   $211.90   $211.90  
  7 purchase totals = $1,029.62       $1,119.4991   $1,119.49   $1,119.45   $1,119.50