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 $79.61   4.292%   $83.0269   $83.03   $83.05   $83.00  
  Purchase #2 $213.48   12.575%   $240.3251   $240.33   $240.35   $240.30  
  Purchase #3 $5.30   13.756%   $6.0291   $6.03   $6.05   $6.00  
  Purchase #4 $227.82   6.290%   $242.1499   $242.15   $242.15   $242.10  
  Purchase #5 $149.62   8.224%   $161.9247   $161.92   $161.90   $161.90  
  Purchase #6 $223.53   9.748%   $245.3197   $245.32   $245.30   $245.30  
  Purchase #7 $85.51   12.840%   $96.4895   $96.49   $96.50   $96.50  
  7 purchase totals = $984.87       $1,075.2649   $1,075.27   $1,075.30   $1,075.10