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 $202.84   6.826%   $216.6859   $216.69   $216.70   $216.70  
  Purchase #2 $232.35   6.580%   $247.6386   $247.64   $247.65   $247.60  
  Purchase #3 $34.84   12.671%   $39.2546   $39.25   $39.25   $39.30  
  Purchase #4 $82.50   8.384%   $89.4168   $89.42   $89.40   $89.40  
  Purchase #5 $163.29   7.425%   $175.4143   $175.41   $175.40   $175.40  
  Purchase #6 $58.73   9.624%   $64.3822   $64.38   $64.40   $64.40  
  Purchase #7 $181.56   8.287%   $196.6059   $196.61   $196.60   $196.60  
  7 purchase totals = $956.11       $1,029.3983   $1,029.40   $1,029.40   $1,029.40