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 $38.26   8.669%   $41.5768   $41.58   $41.60   $41.60  
  Purchase #2 $154.37   11.187%   $171.6394   $171.64   $171.65   $171.60  
  Purchase #3 $96.69   9.402%   $105.7808   $105.78   $105.80   $105.80  
  Purchase #4 $118.54   6.455%   $126.1918   $126.19   $126.20   $126.20  
  Purchase #5 $10.36   5.554%   $10.9354   $10.94   $10.95   $10.90  
  Purchase #6 $233.29   11.160%   $259.3252   $259.33   $259.35   $259.30  
  Purchase #7 $31.60   11.321%   $35.1774   $35.18   $35.20   $35.20  
  7 purchase totals = $683.11       $750.6268   $750.64   $750.75   $750.60