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 $74.88   12.593%   $84.3096   $84.31   $84.30   $84.30  
  Purchase #2 $175.70   9.106%   $191.6992   $191.70   $191.70   $191.70  
  Purchase #3 $25.90   12.854%   $29.2292   $29.23   $29.25   $29.20  
  Purchase #4 $85.29   12.397%   $95.8634   $95.86   $95.85   $95.90  
  Purchase #5 $20.91   4.473%   $21.8453   $21.85   $21.85   $21.80  
  Purchase #6 $238.26   8.742%   $259.0887   $259.09   $259.10   $259.10  
  Purchase #7 $242.55   12.296%   $272.3739   $272.37   $272.35   $272.40  
  7 purchase totals = $863.49       $954.4093   $954.41   $954.40   $954.40