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 $231.47   4.445%   $241.7588   $241.76   $241.75   $241.80  
  Purchase #2 $236.43   11.450%   $263.5012   $263.50   $263.50   $263.50  
  Purchase #3 $156.26   12.619%   $175.9784   $175.98   $176.00   $176.00  
  Purchase #4 $95.27   11.723%   $106.4385   $106.44   $106.45   $106.40  
  Purchase #5 $13.97   8.801%   $15.1995   $15.20   $15.20   $15.20  
  Purchase #6 $66.58   7.121%   $71.3212   $71.32   $71.30   $71.30  
  Purchase #7 $122.69   9.515%   $134.364   $134.36   $134.35   $134.40  
  7 purchase totals = $922.67       $1,008.5616   $1,008.56   $1,008.55   $1,008.60