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 $83.99   13.862%   $95.6327   $95.63   $95.65   $95.60  
  Purchase #2 $149.46   3.142%   $154.156   $154.16   $154.15   $154.20  
  Purchase #3 $71.95   7.803%   $77.5643   $77.56   $77.55   $77.60  
  Purchase #4 $247.99   9.558%   $271.6929   $271.69   $271.70   $271.70  
  Purchase #5 $113.75   13.117%   $128.6706   $128.67   $128.65   $128.70  
  Purchase #6 $134.60   6.646%   $143.5455   $143.55   $143.55   $143.50  
  Purchase #7 $245.52   13.866%   $279.5638   $279.56   $279.55   $279.60  
  7 purchase totals = $1,047.26       $1,150.8258   $1,150.82   $1,150.80   $1,150.90