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 $68.61   9.748%   $75.2981   $75.30   $75.30   $75.30  
  Purchase #2 $167.38   8.451%   $181.5253   $181.53   $181.55   $181.50  
  Purchase #3 $239.55   3.507%   $247.951   $247.95   $247.95   $248.00  
  Purchase #4 $223.34   6.636%   $238.1608   $238.16   $238.15   $238.20  
  Purchase #5 $54.44   11.110%   $60.4883   $60.49   $60.50   $60.50  
  Purchase #6 $17.88   13.473%   $20.289   $20.29   $20.30   $20.30  
  Purchase #7 $243.67   5.114%   $256.1313   $256.13   $256.15   $256.10  
  7 purchase totals = $1,014.87       $1,079.8438   $1,079.85   $1,079.90   $1,079.90