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 $60.32   5.521%   $63.6503   $63.65   $63.65   $63.70  
  Purchase #2 $175.28   12.143%   $196.5643   $196.56   $196.55   $196.60  
  Purchase #3 $190.91   5.295%   $201.0187   $201.02   $201.00   $201.00  
  Purchase #4 $69.30   5.375%   $73.0249   $73.02   $73.00   $73.00  
  Purchase #5 $17.27   6.474%   $18.3881   $18.39   $18.40   $18.40  
  Purchase #6 $66.42   9.655%   $72.8329   $72.83   $72.85   $72.80  
  Purchase #7 $242.60   13.502%   $275.3559   $275.36   $275.35   $275.40  
  7 purchase totals = $822.10       $900.8351   $900.83   $900.80   $900.90