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 $107.55   8.296%   $116.4723   $116.47   $116.45   $116.50  
  Purchase #2 $163.95   11.219%   $182.3436   $182.34   $182.35   $182.30  
  Purchase #3 $30.61   10.414%   $33.7977   $33.80   $33.80   $33.80  
  Purchase #4 $242.32   8.648%   $263.2758   $263.28   $263.30   $263.30  
  Purchase #5 $117.26   10.606%   $129.6966   $129.70   $129.70   $129.70  
  Purchase #6 $165.33   10.395%   $182.5161   $182.52   $182.50   $182.50  
  Purchase #7 $235.97   8.139%   $255.1756   $255.18   $255.20   $255.20  
  7 purchase totals = $1,062.99       $1,163.2777   $1,163.29   $1,163.30   $1,163.30