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 $89.86   5.557%   $94.8535   $94.85   $94.85   $94.90  
  Purchase #2 $240.83   9.371%   $263.3982   $263.40   $263.40   $263.40  
  Purchase #3 $106.55   10.454%   $117.6887   $117.69   $117.70   $117.70  
  Purchase #4 $157.55   5.223%   $165.7788   $165.78   $165.80   $165.80  
  Purchase #5 $152.31   9.859%   $167.3262   $167.33   $167.35   $167.30  
  Purchase #6 $68.40   4.769%   $71.662   $71.66   $71.65   $71.70  
  Purchase #7 $34.75   6.143%   $36.8847   $36.88   $36.90   $36.90  
  7 purchase totals = $850.25       $917.5921   $917.59   $917.65   $917.70