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 $74.34   11.118%   $82.6051   $82.61   $82.60   $82.60  
  Purchase #2 $220.82   7.623%   $237.6531   $237.65   $237.65   $237.70  
  Purchase #3 $161.93   3.395%   $167.4275   $167.43   $167.45   $167.40  
  Purchase #4 $125.81   12.521%   $141.5627   $141.56   $141.55   $141.60  
  Purchase #5 $207.98   5.871%   $220.1905   $220.19   $220.20   $220.20  
  Purchase #6 $84.45   5.623%   $89.1986   $89.20   $89.20   $89.20  
  Purchase #7 $14.61   9.257%   $15.9624   $15.96   $15.95   $16.00  
  7 purchase totals = $889.94       $954.5999   $954.60   $954.60   $954.70