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 $118.39   5.372%   $124.7499   $124.75   $124.75   $124.70  
  Purchase #2 $163.82   10.402%   $180.8606   $180.86   $180.85   $180.90  
  Purchase #3 $128.35   6.676%   $136.9186   $136.92   $136.90   $136.90  
  Purchase #4 $220.29   12.630%   $248.1126   $248.11   $248.10   $248.10  
  Purchase #5 $156.89   3.767%   $162.8   $162.80   $162.80   $162.80  
  Purchase #6 $96.68   13.113%   $109.3576   $109.36   $109.35   $109.40  
  Purchase #7 $146.75   9.648%   $160.9084   $160.91   $160.90   $160.90  
  7 purchase totals = $1,031.17       $1,123.7077   $1,123.71   $1,123.65   $1,123.70