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 $223.26   10.547%   $246.8072   $246.81   $246.80   $246.80  
  Purchase #2 $241.97   5.394%   $255.0219   $255.02   $255.00   $255.00  
  Purchase #3 $41.43   12.456%   $46.5905   $46.59   $46.60   $46.60  
  Purchase #4 $242.40   9.823%   $266.211   $266.21   $266.20   $266.20  
  Purchase #5 $87.79   3.365%   $90.7441   $90.74   $90.75   $90.70  
  Purchase #6 $140.92   3.456%   $145.7902   $145.79   $145.80   $145.80  
  Purchase #7 $189.28   3.703%   $196.289   $196.29   $196.30   $196.30  
  7 purchase totals = $1,167.05       $1,247.4539   $1,247.45   $1,247.45   $1,247.40