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 $97.27   6.300%   $103.398   $103.40   $103.40   $103.40  
  Purchase #2 $243.34   5.110%   $255.7747   $255.77   $255.75   $255.80  
  Purchase #3 $227.94   7.782%   $245.6783   $245.68   $245.70   $245.70  
  Purchase #4 $43.61   9.569%   $47.783   $47.78   $47.80   $47.80  
  Purchase #5 $220.84   9.314%   $241.409   $241.41   $241.40   $241.40  
  Purchase #6 $120.42   3.379%   $124.489   $124.49   $124.50   $124.50  
  Purchase #7 $245.82   7.291%   $263.7427   $263.74   $263.75   $263.70  
  7 purchase totals = $1,199.24       $1,282.2747   $1,282.27   $1,282.30   $1,282.30