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 $218.72   13.398%   $248.0241   $248.02   $248.00   $248.00  
  Purchase #2 $212.97   7.466%   $228.8703   $228.87   $228.85   $228.90  
  Purchase #3 $88.31   5.263%   $92.9578   $92.96   $92.95   $93.00  
  Purchase #4 $186.75   5.442%   $196.9129   $196.91   $196.90   $196.90  
  Purchase #5 $67.37   8.366%   $73.0062   $73.01   $73.00   $73.00  
  Purchase #6 $53.48   5.605%   $56.4776   $56.48   $56.50   $56.50  
  Purchase #7 $222.47   3.205%   $229.6002   $229.60   $229.60   $229.60  
  7 purchase totals = $1,050.07       $1,125.8491   $1,125.85   $1,125.80   $1,125.90