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 $232.58   13.515%   $264.0132   $264.01   $264.00   $264.00  
  Purchase #2 $148.71   9.153%   $162.3214   $162.32   $162.30   $162.30  
  Purchase #3 $245.82   4.609%   $257.1498   $257.15   $257.15   $257.10  
  Purchase #4 $204.90   5.583%   $216.3396   $216.34   $216.35   $216.30  
  Purchase #5 $49.99   5.478%   $52.7285   $52.73   $52.75   $52.70  
  Purchase #6 $31.79   13.718%   $36.151   $36.15   $36.15   $36.20  
  Purchase #7 $73.57   12.800%   $82.987   $82.99   $83.00   $83.00  
  7 purchase totals = $987.36       $1,071.6905   $1,071.69   $1,071.70   $1,071.60