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 $202.59   10.836%   $224.5427   $224.54   $224.55   $224.50  
  Purchase #2 $88.32   5.578%   $93.2465   $93.25   $93.25   $93.20  
  Purchase #3 $36.76   5.171%   $38.6609   $38.66   $38.65   $38.70  
  Purchase #4 $220.68   6.412%   $234.83   $234.83   $234.85   $234.80  
  Purchase #5 $118.91   11.474%   $132.5537   $132.55   $132.55   $132.60  
  Purchase #6 $87.88   9.681%   $96.3877   $96.39   $96.40   $96.40  
  Purchase #7 $221.43   11.339%   $246.5379   $246.54   $246.55   $246.50  
  7 purchase totals = $976.57       $1,066.7594   $1,066.76   $1,066.80   $1,066.70