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 $181.34   8.751%   $197.2091   $197.21   $197.20   $197.20  
  Purchase #2 $95.75   10.611%   $105.91   $105.91   $105.90   $105.90  
  Purchase #3 $16.90   3.471%   $17.4866   $17.49   $17.50   $17.50  
  Purchase #4 $87.85   11.843%   $98.2541   $98.25   $98.25   $98.30  
  Purchase #5 $161.34   5.316%   $169.9168   $169.92   $169.90   $169.90  
  Purchase #6 $202.97   9.828%   $222.9179   $222.92   $222.90   $222.90  
  Purchase #7 $34.35   5.758%   $36.3279   $36.33   $36.35   $36.30  
  7 purchase totals = $780.50       $848.0224   $848.03   $848.00   $848.00