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 $76.62   13.865%   $87.2434   $87.24   $87.25   $87.20  
  Purchase #2 $97.52   6.667%   $104.0217   $104.02   $104.00   $104.00  
  Purchase #3 $78.32   6.696%   $83.5643   $83.56   $83.55   $83.60  
  Purchase #4 $241.28   13.791%   $274.5549   $274.55   $274.55   $274.60  
  Purchase #5 $87.28   10.824%   $96.7272   $96.73   $96.75   $96.70  
  Purchase #6 $30.98   13.177%   $35.0622   $35.06   $35.05   $35.10  
  Purchase #7 $231.90   6.143%   $246.1456   $246.15   $246.15   $246.10  
  7 purchase totals = $843.90       $927.3193   $927.31   $927.30   $927.30