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 $233.97   8.240%   $253.2491   $253.25   $253.25   $253.20  
  Purchase #2 $90.78   5.849%   $96.0897   $96.09   $96.10   $96.10  
  Purchase #3 $28.48   12.580%   $32.0628   $32.06   $32.05   $32.10  
  Purchase #4 $157.38   6.524%   $167.6475   $167.65   $167.65   $167.60  
  Purchase #5 $69.55   11.596%   $77.615   $77.62   $77.60   $77.60  
  Purchase #6 $224.61   9.856%   $246.7476   $246.75   $246.75   $246.70  
  Purchase #7 $131.96   13.108%   $149.2573   $149.26   $149.25   $149.30  
  7 purchase totals = $936.73       $1,022.6690   $1,022.68   $1,022.65   $1,022.60