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 $188.59   8.669%   $204.9389   $204.94   $204.95   $204.90  
  Purchase #2 $175.83   10.175%   $193.7207   $193.72   $193.70   $193.70  
  Purchase #3 $140.93   8.306%   $152.6356   $152.64   $152.65   $152.60  
  Purchase #4 $32.39   11.418%   $36.0883   $36.09   $36.10   $36.10  
  Purchase #5 $180.85   6.502%   $192.6089   $192.61   $192.60   $192.60  
  Purchase #6 $49.93   9.782%   $54.8142   $54.81   $54.80   $54.80  
  Purchase #7 $203.46   4.658%   $212.9372   $212.94   $212.95   $212.90  
  7 purchase totals = $971.98       $1,047.7438   $1,047.75   $1,047.75   $1,047.60