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 $74.76   13.691%   $84.9954   $85.00   $85.00   $85.00  
  Purchase #2 $203.74   8.298%   $220.6463   $220.65   $220.65   $220.60  
  Purchase #3 $118.87   6.568%   $126.6774   $126.68   $126.70   $126.70  
  Purchase #4 $132.77   10.337%   $146.4944   $146.49   $146.50   $146.50  
  Purchase #5 $181.27   3.555%   $187.7141   $187.71   $187.70   $187.70  
  Purchase #6 $13.66   12.459%   $15.3619   $15.36   $15.35   $15.40  
  Purchase #7 $154.70   5.192%   $162.732   $162.73   $162.75   $162.70  
  7 purchase totals = $879.77       $944.6215   $944.62   $944.65   $944.60