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 $105.92   12.815%   $119.4936   $119.49   $119.50   $119.50  
  Purchase #2 $152.63   13.319%   $172.9588   $172.96   $172.95   $173.00  
  Purchase #3 $151.85   6.421%   $161.6003   $161.60   $161.60   $161.60  
  Purchase #4 $137.94   9.255%   $150.7063   $150.71   $150.70   $150.70  
  Purchase #5 $215.46   4.171%   $224.4468   $224.45   $224.45   $224.40  
  Purchase #6 $47.51   11.531%   $52.9884   $52.99   $53.00   $53.00  
  Purchase #7 $161.88   6.751%   $172.8085   $172.81   $172.80   $172.80  
  7 purchase totals = $973.19       $1,055.0027   $1,055.01   $1,055.00   $1,055.00