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 $212.77   6.653%   $226.9256   $226.93   $226.95   $226.90  
  Purchase #2 $204.39   8.220%   $221.1909   $221.19   $221.20   $221.20  
  Purchase #3 $62.26   8.870%   $67.7825   $67.78   $67.80   $67.80  
  Purchase #4 $155.53   9.491%   $170.2914   $170.29   $170.30   $170.30  
  Purchase #5 $244.74   11.608%   $273.1494   $273.15   $273.15   $273.10  
  Purchase #6 $51.45   6.109%   $54.5931   $54.59   $54.60   $54.60  
  Purchase #7 $139.63   6.162%   $148.234   $148.23   $148.25   $148.20  
  7 purchase totals = $1,070.77       $1,162.1669   $1,162.16   $1,162.25   $1,162.10