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 $246.76   8.542%   $267.8382   $267.84   $267.85   $267.80  
  Purchase #2 $71.28   5.494%   $75.1961   $75.20   $75.20   $75.20  
  Purchase #3 $245.50   12.173%   $275.3847   $275.38   $275.40   $275.40  
  Purchase #4 $170.46   8.860%   $185.5628   $185.56   $185.55   $185.60  
  Purchase #5 $107.75   12.562%   $121.2856   $121.29   $121.30   $121.30  
  Purchase #6 $186.83   10.390%   $206.2416   $206.24   $206.25   $206.20  
  Purchase #7 $29.57   12.192%   $33.1752   $33.18   $33.20   $33.20  
  7 purchase totals = $1,058.15       $1,164.6842   $1,164.69   $1,164.75   $1,164.70