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 $91.58   3.258%   $94.5637   $94.56   $94.55   $94.60  
  Purchase #2 $68.71   7.227%   $73.6757   $73.68   $73.70   $73.70  
  Purchase #3 $158.37   6.246%   $168.2618   $168.26   $168.25   $168.30  
  Purchase #4 $7.98   7.680%   $8.5929   $8.59   $8.60   $8.60  
  Purchase #5 $226.97   6.321%   $241.3168   $241.32   $241.30   $241.30  
  Purchase #6 $157.40   6.294%   $167.3068   $167.31   $167.30   $167.30  
  Purchase #7 $217.78   4.842%   $228.3249   $228.32   $228.30   $228.30  
  7 purchase totals = $928.79       $982.0426   $982.04   $982.00   $982.10