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 $129.75   3.454%   $134.2316   $134.23   $134.25   $134.20  
  Purchase #2 $192.59   11.443%   $214.6281   $214.63   $214.65   $214.60  
  Purchase #3 $65.35   11.135%   $72.6267   $72.63   $72.65   $72.60  
  Purchase #4 $57.62   13.777%   $65.5583   $65.56   $65.55   $65.60  
  Purchase #5 $43.55   9.276%   $47.5897   $47.59   $47.60   $47.60  
  Purchase #6 $119.49   6.162%   $126.853   $126.85   $126.85   $126.90  
  Purchase #7 $224.48   10.314%   $247.6329   $247.63   $247.65   $247.60  
  7 purchase totals = $832.83       $909.1203   $909.12   $909.20   $909.10