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 $162.93   13.699%   $185.2498   $185.25   $185.25   $185.20  
  Purchase #2 $70.25   3.129%   $72.4481   $72.45   $72.45   $72.40  
  Purchase #3 $43.52   8.843%   $47.3685   $47.37   $47.35   $47.40  
  Purchase #4 $220.67   4.222%   $229.9867   $229.99   $230.00   $230.00  
  Purchase #5 $113.43   4.399%   $118.4198   $118.42   $118.40   $118.40  
  Purchase #6 $127.26   6.135%   $135.0674   $135.07   $135.05   $135.10  
  Purchase #7 $219.90   10.227%   $242.3892   $242.39   $242.40   $242.40  
  7 purchase totals = $957.96       $1,030.9295   $1,030.94   $1,030.90   $1,030.90