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 $86.77   10.194%   $95.6153   $95.62   $95.60   $95.60  
  Purchase #2 $240.64   6.398%   $256.0361   $256.04   $256.05   $256.00  
  Purchase #3 $166.35   13.122%   $188.1784   $188.18   $188.20   $188.20  
  Purchase #4 $65.79   10.360%   $72.6058   $72.61   $72.60   $72.60  
  Purchase #5 $52.54   9.373%   $57.4646   $57.46   $57.45   $57.50  
  Purchase #6 $246.95   9.819%   $271.198   $271.20   $271.20   $271.20  
  Purchase #7 $99.96   8.199%   $108.1557   $108.16   $108.15   $108.20  
  7 purchase totals = $959.00       $1,049.2539   $1,049.27   $1,049.25   $1,049.30