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 $85.58   7.797%   $92.2527   $92.25   $92.25   $92.30  
  Purchase #2 $21.84   6.711%   $23.3057   $23.31   $23.30   $23.30  
  Purchase #3 $120.58   8.220%   $130.4917   $130.49   $130.50   $130.50  
  Purchase #4 $67.28   3.542%   $69.6631   $69.66   $69.65   $69.70  
  Purchase #5 $173.42   12.345%   $194.8287   $194.83   $194.85   $194.80  
  Purchase #6 $199.72   13.358%   $226.3986   $226.40   $226.40   $226.40  
  Purchase #7 $138.73   13.172%   $157.0035   $157.00   $157.00   $157.00  
  7 purchase totals = $807.15       $893.9440   $893.94   $893.95   $894.00