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 $40.65   9.732%   $44.6061   $44.61   $44.60   $44.60  
  Purchase #2 $241.53   4.635%   $252.7249   $252.72   $252.70   $252.70  
  Purchase #3 $224.27   9.118%   $244.7189   $244.72   $244.70   $244.70  
  Purchase #4 $146.67   11.340%   $163.3024   $163.30   $163.30   $163.30  
  Purchase #5 $222.85   9.414%   $243.8291   $243.83   $243.85   $243.80  
  Purchase #6 $162.35   11.532%   $181.0722   $181.07   $181.05   $181.10  
  Purchase #7 $107.68   5.539%   $113.6444   $113.64   $113.65   $113.60  
  7 purchase totals = $1,146.00       $1,243.8980   $1,243.89   $1,243.85   $1,243.80