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 $28.67   13.482%   $32.5353   $32.54   $32.55   $32.50  
  Purchase #2 $135.34   13.694%   $153.8735   $153.87   $153.85   $153.90  
  Purchase #3 $123.38   8.405%   $133.7501   $133.75   $133.75   $133.80  
  Purchase #4 $154.52   5.617%   $163.1994   $163.20   $163.20   $163.20  
  Purchase #5 $165.89   5.694%   $175.3358   $175.34   $175.35   $175.30  
  Purchase #6 $182.96   9.245%   $199.8747   $199.87   $199.85   $199.90  
  Purchase #7 $192.91   3.428%   $199.523   $199.52   $199.50   $199.50  
  7 purchase totals = $983.67       $1,058.0918   $1,058.09   $1,058.05   $1,058.10