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 $55.51   5.821%   $58.7412   $58.74   $58.75   $58.70  
  Purchase #2 $207.69   3.672%   $215.3164   $215.32   $215.30   $215.30  
  Purchase #3 $167.85   3.464%   $173.6643   $173.66   $173.65   $173.70  
  Purchase #4 $93.86   5.349%   $98.8806   $98.88   $98.90   $98.90  
  Purchase #5 $211.97   3.661%   $219.7302   $219.73   $219.75   $219.70  
  Purchase #6 $165.94   12.258%   $186.2809   $186.28   $186.30   $186.30  
  Purchase #7 $222.33   7.122%   $238.1643   $238.16   $238.15   $238.20  
  7 purchase totals = $1,125.15       $1,190.7779   $1,190.77   $1,190.80   $1,190.80