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 $75.81   8.591%   $82.3228   $82.32   $82.30   $82.30  
  Purchase #2 $213.77   9.685%   $234.4736   $234.47   $234.45   $234.50  
  Purchase #3 $31.50   8.221%   $34.0896   $34.09   $34.10   $34.10  
  Purchase #4 $86.35   7.396%   $92.7364   $92.74   $92.75   $92.70  
  Purchase #5 $217.52   13.170%   $246.1674   $246.17   $246.15   $246.20  
  Purchase #6 $234.33   6.155%   $248.753   $248.75   $248.75   $248.80  
  Purchase #7 $126.37   12.624%   $142.3229   $142.32   $142.30   $142.30  
  7 purchase totals = $985.65       $1,080.8657   $1,080.86   $1,080.80   $1,080.90