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 $207.75   10.725%   $230.0312   $230.03   $230.05   $230.00  
  Purchase #2 $79.96   7.336%   $85.8259   $85.83   $85.85   $85.80  
  Purchase #3 $80.99   12.277%   $90.9331   $90.93   $90.95   $90.90  
  Purchase #4 $173.39   6.616%   $184.8615   $184.86   $184.85   $184.90  
  Purchase #5 $123.29   12.703%   $138.9515   $138.95   $138.95   $139.00  
  Purchase #6 $151.67   6.250%   $161.1494   $161.15   $161.15   $161.10  
  Purchase #7 $122.32   8.598%   $132.8371   $132.84   $132.85   $132.80  
  7 purchase totals = $939.37       $1,024.5897   $1,024.59   $1,024.65   $1,024.50