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 $74.54   12.479%   $83.8418   $83.84   $83.85   $83.80  
  Purchase #2 $70.51   4.735%   $73.8486   $73.85   $73.85   $73.80  
  Purchase #3 $89.83   13.523%   $101.9777   $101.98   $102.00   $102.00  
  Purchase #4 $250.91   8.363%   $271.8936   $271.89   $271.90   $271.90  
  Purchase #5 $112.30   8.578%   $121.9331   $121.93   $121.95   $121.90  
  Purchase #6 $153.64   9.793%   $168.686   $168.69   $168.70   $168.70  
  Purchase #7 $237.72   13.449%   $269.691   $269.69   $269.70   $269.70  
  7 purchase totals = $989.45       $1,091.8718   $1,091.87   $1,091.95   $1,091.80