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 $48.94   8.368%   $53.0353   $53.04   $53.05   $53.00  
  Purchase #2 $219.93   11.492%   $245.2044   $245.20   $245.20   $245.20  
  Purchase #3 $62.53   13.218%   $70.7952   $70.80   $70.80   $70.80  
  Purchase #4 $165.82   10.493%   $183.2195   $183.22   $183.20   $183.20  
  Purchase #5 $217.66   11.594%   $242.8955   $242.90   $242.90   $242.90  
  Purchase #6 $41.81   4.214%   $43.5719   $43.57   $43.55   $43.60  
  Purchase #7 $47.79   13.383%   $54.1857   $54.19   $54.20   $54.20  
  7 purchase totals = $804.48       $892.9075   $892.92   $892.90   $892.90