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 $92.26   4.730%   $96.6239   $96.62   $96.60   $96.60  
  Purchase #2 $136.70   6.747%   $145.9231   $145.92   $145.90   $145.90  
  Purchase #3 $108.95   3.460%   $112.7197   $112.72   $112.70   $112.70  
  Purchase #4 $219.26   4.818%   $229.8239   $229.82   $229.80   $229.80  
  Purchase #5 $185.40   8.528%   $201.2109   $201.21   $201.20   $201.20  
  Purchase #6 $128.43   12.835%   $144.914   $144.91   $144.90   $144.90  
  Purchase #7 $93.66   9.106%   $102.1887   $102.19   $102.20   $102.20  
  7 purchase totals = $964.66       $1,033.4042   $1,033.39   $1,033.30   $1,033.30