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 $198.43   12.868%   $223.964   $223.96   $223.95   $224.00  
  Purchase #2 $207.89   8.153%   $224.8393   $224.84   $224.85   $224.80  
  Purchase #3 $157.97   4.410%   $164.9365   $164.94   $164.95   $164.90  
  Purchase #4 $200.60   9.448%   $219.5527   $219.55   $219.55   $219.60  
  Purchase #5 $19.53   6.756%   $20.8494   $20.85   $20.85   $20.80  
  Purchase #6 $10.41   5.792%   $11.0129   $11.01   $11.00   $11.00  
  Purchase #7 $188.41   12.664%   $212.2702   $212.27   $212.25   $212.30  
  7 purchase totals = $983.24       $1,077.4250   $1,077.42   $1,077.40   $1,077.40