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 $89.46   10.348%   $98.7173   $98.72   $98.70   $98.70  
  Purchase #2 $216.86   13.558%   $246.2619   $246.26   $246.25   $246.30  
  Purchase #3 $104.47   7.199%   $111.9908   $111.99   $112.00   $112.00  
  Purchase #4 $181.50   6.698%   $193.6569   $193.66   $193.65   $193.70  
  Purchase #5 $104.42   9.441%   $114.2783   $114.28   $114.30   $114.30  
  Purchase #6 $201.50   6.755%   $215.1113   $215.11   $215.10   $215.10  
  Purchase #7 $20.34   11.414%   $22.6616   $22.66   $22.65   $22.70  
  7 purchase totals = $918.55       $1,002.6781   $1,002.68   $1,002.65   $1,002.80