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 $213.86   11.642%   $238.7576   $238.76   $238.75   $238.80  
  Purchase #2 $169.93   3.422%   $175.745   $175.75   $175.75   $175.70  
  Purchase #3 $91.34   12.632%   $102.8781   $102.88   $102.90   $102.90  
  Purchase #4 $73.90   7.659%   $79.56   $79.56   $79.55   $79.60  
  Purchase #5 $6.48   4.736%   $6.7869   $6.79   $6.80   $6.80  
  Purchase #6 $91.50   5.445%   $96.4822   $96.48   $96.50   $96.50  
  Purchase #7 $246.68   5.555%   $260.3831   $260.38   $260.40   $260.40  
  7 purchase totals = $893.69       $960.5929   $960.60   $960.65   $960.70