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 $168.84   4.556%   $176.5324   $176.53   $176.55   $176.50  
  Purchase #2 $59.64   8.379%   $64.6372   $64.64   $64.65   $64.60  
  Purchase #3 $146.85   4.624%   $153.6403   $153.64   $153.65   $153.60  
  Purchase #4 $63.59   9.488%   $69.6234   $69.62   $69.60   $69.60  
  Purchase #5 $245.54   7.805%   $264.7044   $264.70   $264.70   $264.70  
  Purchase #6 $182.60   11.191%   $203.0348   $203.03   $203.05   $203.00  
  Purchase #7 $73.30   13.618%   $83.282   $83.28   $83.30   $83.30  
  7 purchase totals = $940.36       $1,015.4545   $1,015.44   $1,015.50   $1,015.30