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 $66.93   13.458%   $75.9374   $75.94   $75.95   $75.90  
  Purchase #2 $197.94   10.725%   $219.1691   $219.17   $219.15   $219.20  
  Purchase #3 $248.31   9.750%   $272.5202   $272.52   $272.50   $272.50  
  Purchase #4 $68.53   5.326%   $72.1799   $72.18   $72.20   $72.20  
  Purchase #5 $29.55   5.657%   $31.2216   $31.22   $31.20   $31.20  
  Purchase #6 $217.57   11.233%   $242.0096   $242.01   $242.00   $242.00  
  Purchase #7 $233.93   8.619%   $254.0924   $254.09   $254.10   $254.10  
  7 purchase totals = $1,062.76       $1,167.1302   $1,167.13   $1,167.10   $1,167.10