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 $49.86   12.188%   $55.9369   $55.94   $55.95   $55.90  
  Purchase #2 $40.74   12.384%   $45.7852   $45.79   $45.80   $45.80  
  Purchase #3 $232.93   5.273%   $245.2124   $245.21   $245.20   $245.20  
  Purchase #4 $140.53   5.741%   $148.5978   $148.60   $148.60   $148.60  
  Purchase #5 $184.89   11.599%   $206.3354   $206.34   $206.35   $206.30  
  Purchase #6 $171.26   12.170%   $192.1023   $192.10   $192.10   $192.10  
  Purchase #7 $123.72   13.393%   $140.2898   $140.29   $140.30   $140.30  
  7 purchase totals = $943.93       $1,034.2598   $1,034.27   $1,034.30   $1,034.20