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 $153.47   8.608%   $166.6807   $166.68   $166.70   $166.70  
  Purchase #2 $203.68   11.688%   $227.4861   $227.49   $227.50   $227.50  
  Purchase #3 $170.85   8.206%   $184.87   $184.87   $184.85   $184.90  
  Purchase #4 $64.56   7.576%   $69.4511   $69.45   $69.45   $69.50  
  Purchase #5 $219.47   11.198%   $244.0463   $244.05   $244.05   $244.00  
  Purchase #6 $57.89   8.189%   $62.6306   $62.63   $62.65   $62.60  
  Purchase #7 $69.79   10.774%   $77.3092   $77.31   $77.30   $77.30  
  7 purchase totals = $939.71       $1,032.4740   $1,032.48   $1,032.50   $1,032.50