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 $178.63   12.830%   $201.5482   $201.55   $201.55   $201.50  
  Purchase #2 $101.42   7.827%   $109.3581   $109.36   $109.35   $109.40  
  Purchase #3 $200.54   4.737%   $210.0396   $210.04   $210.05   $210.00  
  Purchase #4 $55.28   9.560%   $60.5648   $60.56   $60.55   $60.60  
  Purchase #5 $99.65   8.740%   $108.3594   $108.36   $108.35   $108.40  
  Purchase #6 $189.30   4.451%   $197.7257   $197.73   $197.75   $197.70  
  Purchase #7 $144.87   13.761%   $164.8056   $164.81   $164.80   $164.80  
  7 purchase totals = $969.69       $1,052.4014   $1,052.41   $1,052.40   $1,052.40