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 $55.26   3.277%   $57.0709   $57.07   $57.05   $57.10  
  Purchase #2 $228.83   8.135%   $247.4453   $247.45   $247.45   $247.40  
  Purchase #3 $209.91   6.858%   $224.3056   $224.31   $224.30   $224.30  
  Purchase #4 $158.26   10.599%   $175.034   $175.03   $175.05   $175.00  
  Purchase #5 $75.57   10.656%   $83.6227   $83.62   $83.60   $83.60  
  Purchase #6 $242.62   7.834%   $261.6269   $261.63   $261.65   $261.60  
  Purchase #7 $7.98   8.121%   $8.6281   $8.63   $8.65   $8.60  
  7 purchase totals = $978.43       $1,057.7335   $1,057.74   $1,057.75   $1,057.60