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 $52.29   11.279%   $58.1878   $58.19   $58.20   $58.20  
  Purchase #2 $243.54   11.277%   $271.004   $271.00   $271.00   $271.00  
  Purchase #3 $151.99   12.738%   $171.3505   $171.35   $171.35   $171.40  
  Purchase #4 $228.62   5.476%   $241.1392   $241.14   $241.15   $241.10  
  Purchase #5 $245.77   13.151%   $278.0912   $278.09   $278.10   $278.10  
  Purchase #6 $229.74   6.509%   $244.6938   $244.69   $244.70   $244.70  
  Purchase #7 $196.77   12.495%   $221.3564   $221.36   $221.35   $221.40  
  7 purchase totals = $1,348.72       $1,485.8229   $1,485.82   $1,485.85   $1,485.90