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 $148.35   4.609%   $155.1875   $155.19   $155.20   $155.20  
  Purchase #2 $224.55   8.202%   $242.9676   $242.97   $242.95   $243.00  
  Purchase #3 $183.34   9.294%   $200.3796   $200.38   $200.40   $200.40  
  Purchase #4 $128.28   9.279%   $140.1831   $140.18   $140.20   $140.20  
  Purchase #5 $170.87   3.442%   $176.7513   $176.75   $176.75   $176.80  
  Purchase #6 $103.89   4.722%   $108.7957   $108.80   $108.80   $108.80  
  Purchase #7 $81.35   13.722%   $92.5128   $92.51   $92.50   $92.50  
  7 purchase totals = $1,040.63       $1,116.7776   $1,116.78   $1,116.80   $1,116.90