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 $65.76   5.419%   $69.3235   $69.32   $69.30   $69.30  
  Purchase #2 $215.83   11.533%   $240.7217   $240.72   $240.70   $240.70  
  Purchase #3 $204.60   12.114%   $229.3852   $229.39   $229.40   $229.40  
  Purchase #4 $156.75   9.482%   $171.613   $171.61   $171.60   $171.60  
  Purchase #5 $16.72   10.195%   $18.4246   $18.42   $18.40   $18.40  
  Purchase #6 $8.67   10.252%   $9.5588   $9.56   $9.55   $9.60  
  Purchase #7 $244.90   9.373%   $267.8545   $267.85   $267.85   $267.90  
  7 purchase totals = $913.23       $1,006.8813   $1,006.87   $1,006.80   $1,006.90