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 $226.84   12.212%   $254.5417   $254.54   $254.55   $254.50  
  Purchase #2 $140.76   4.685%   $147.3546   $147.35   $147.35   $147.40  
  Purchase #3 $12.88   13.491%   $14.6176   $14.62   $14.60   $14.60  
  Purchase #4 $225.79   11.346%   $251.4081   $251.41   $251.40   $251.40  
  Purchase #5 $84.29   8.213%   $91.2127   $91.21   $91.20   $91.20  
  Purchase #6 $63.44   13.502%   $72.0057   $72.01   $72.00   $72.00  
  Purchase #7 $180.96   3.847%   $187.9215   $187.92   $187.90   $187.90  
  7 purchase totals = $934.96       $1,019.0619   $1,019.06   $1,019.00   $1,019.00