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 $104.96   12.305%   $117.8753   $117.88   $117.90   $117.90  
  Purchase #2 $90.81   6.120%   $96.3676   $96.37   $96.35   $96.40  
  Purchase #3 $152.60   5.370%   $160.7946   $160.79   $160.80   $160.80  
  Purchase #4 $192.63   5.658%   $203.529   $203.53   $203.55   $203.50  
  Purchase #5 $55.68   12.461%   $62.6183   $62.62   $62.60   $62.60  
  Purchase #6 $92.77   10.571%   $102.5767   $102.58   $102.60   $102.60  
  Purchase #7 $108.53   7.535%   $116.7077   $116.71   $116.70   $116.70  
  7 purchase totals = $797.98       $860.4692   $860.48   $860.50   $860.50