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 $85.26   8.474%   $92.4849   $92.48   $92.50   $92.50  
  Purchase #2 $248.99   10.521%   $275.1862   $275.19   $275.20   $275.20  
  Purchase #3 $111.84   4.678%   $117.0719   $117.07   $117.05   $117.10  
  Purchase #4 $19.53   5.297%   $20.5645   $20.56   $20.55   $20.60  
  Purchase #5 $62.93   6.587%   $67.0752   $67.08   $67.10   $67.10  
  Purchase #6 $211.99   3.655%   $219.7382   $219.74   $219.75   $219.70  
  Purchase #7 $29.36   11.582%   $32.7605   $32.76   $32.75   $32.80  
  7 purchase totals = $769.90       $824.8814   $824.88   $824.90   $825.00