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 $68.97   9.612%   $75.5994   $75.60   $75.60   $75.60  
  Purchase #2 $190.87   13.569%   $216.7692   $216.77   $216.75   $216.80  
  Purchase #3 $210.77   7.544%   $226.6705   $226.67   $226.65   $226.70  
  Purchase #4 $20.83   5.198%   $21.9127   $21.91   $21.90   $21.90  
  Purchase #5 $162.86   6.485%   $173.4215   $173.42   $173.40   $173.40  
  Purchase #6 $87.84   3.760%   $91.1428   $91.14   $91.15   $91.10  
  Purchase #7 $187.76   11.813%   $209.9401   $209.94   $209.95   $209.90  
  7 purchase totals = $929.90       $1,015.4562   $1,015.45   $1,015.40   $1,015.40