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 $244.77   13.156%   $276.9719   $276.97   $276.95   $277.00  
  Purchase #2 $134.87   8.239%   $145.9819   $145.98   $146.00   $146.00  
  Purchase #3 $217.83   4.654%   $227.9678   $227.97   $227.95   $228.00  
  Purchase #4 $141.64   8.486%   $153.6596   $153.66   $153.65   $153.70  
  Purchase #5 $116.63   10.287%   $128.6277   $128.63   $128.65   $128.60  
  Purchase #6 $174.26   7.859%   $187.9551   $187.96   $187.95   $188.00  
  Purchase #7 $64.47   11.184%   $71.6803   $71.68   $71.70   $71.70  
  7 purchase totals = $1,094.47       $1,192.8443   $1,192.85   $1,192.85   $1,193.00