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 $88.61   4.119%   $92.2598   $92.26   $92.25   $92.30  
  Purchase #2 $161.64   12.623%   $182.0438   $182.04   $182.05   $182.00  
  Purchase #3 $200.29   4.559%   $209.4212   $209.42   $209.40   $209.40  
  Purchase #4 $155.66   6.499%   $165.7763   $165.78   $165.80   $165.80  
  Purchase #5 $128.62   6.572%   $137.0729   $137.07   $137.05   $137.10  
  Purchase #6 $198.83   12.423%   $223.5307   $223.53   $223.55   $223.50  
  Purchase #7 $236.46   9.616%   $259.198   $259.20   $259.20   $259.20  
  7 purchase totals = $1,170.11       $1,269.3027   $1,269.30   $1,269.30   $1,269.30