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 $91.64   6.608%   $97.6956   $97.70   $97.70   $97.70  
  Purchase #2 $12.56   5.706%   $13.2767   $13.28   $13.30   $13.30  
  Purchase #3 $228.74   11.348%   $254.6974   $254.70   $254.70   $254.70  
  Purchase #4 $17.50   5.155%   $18.4021   $18.40   $18.40   $18.40  
  Purchase #5 $155.75   4.831%   $163.2743   $163.27   $163.25   $163.30  
  Purchase #6 $109.97   9.739%   $120.68   $120.68   $120.70   $120.70  
  Purchase #7 $91.71   4.815%   $96.1258   $96.13   $96.15   $96.10  
  7 purchase totals = $707.87       $764.1519   $764.16   $764.20   $764.20