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 $201.60   12.737%   $227.2778   $227.28   $227.30   $227.30  
  Purchase #2 $95.31   8.554%   $103.4628   $103.46   $103.45   $103.50  
  Purchase #3 $163.47   11.317%   $181.9699   $181.97   $181.95   $182.00  
  Purchase #4 $131.26   13.455%   $148.921   $148.92   $148.90   $148.90  
  Purchase #5 $109.41   8.753%   $118.9867   $118.99   $119.00   $119.00  
  Purchase #6 $120.89   3.368%   $124.9616   $124.96   $124.95   $125.00  
  Purchase #7 $190.43   8.381%   $206.3899   $206.39   $206.40   $206.40  
  7 purchase totals = $1,012.37       $1,111.9697   $1,111.97   $1,111.95   $1,112.10