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 $170.29   9.604%   $186.6447   $186.64   $186.65   $186.60  
  Purchase #2 $220.42   4.268%   $229.8275   $229.83   $229.85   $229.80  
  Purchase #3 $148.45   11.707%   $165.829   $165.83   $165.85   $165.80  
  Purchase #4 $44.39   8.369%   $48.105   $48.11   $48.10   $48.10  
  Purchase #5 $118.87   9.666%   $130.36   $130.36   $130.35   $130.40  
  Purchase #6 $222.32   10.725%   $246.1638   $246.16   $246.15   $246.20  
  Purchase #7 $135.99   4.613%   $142.2632   $142.26   $142.25   $142.30  
  7 purchase totals = $1,060.73       $1,149.1932   $1,149.19   $1,149.20   $1,149.20