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 $50.47   5.703%   $53.3483   $53.35   $53.35   $53.30  
  Purchase #2 $215.74   8.557%   $234.2009   $234.20   $234.20   $234.20  
  Purchase #3 $116.52   12.842%   $131.4835   $131.48   $131.50   $131.50  
  Purchase #4 $176.36   10.114%   $194.1971   $194.20   $194.20   $194.20  
  Purchase #5 $126.88   11.859%   $141.9267   $141.93   $141.95   $141.90  
  Purchase #6 $187.57   6.761%   $200.2516   $200.25   $200.25   $200.30  
  Purchase #7 $143.84   7.669%   $154.8711   $154.87   $154.85   $154.90  
  7 purchase totals = $1,017.38       $1,110.2792   $1,110.28   $1,110.30   $1,110.30