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 $244.99   4.460%   $255.9166   $255.92   $255.90   $255.90  
  Purchase #2 $163.71   12.712%   $184.5208   $184.52   $184.50   $184.50  
  Purchase #3 $69.79   5.437%   $73.5845   $73.58   $73.60   $73.60  
  Purchase #4 $79.54   7.168%   $85.2414   $85.24   $85.25   $85.20  
  Purchase #5 $6.36   5.350%   $6.7003   $6.70   $6.70   $6.70  
  Purchase #6 $209.95   7.553%   $225.8075   $225.81   $225.80   $225.80  
  Purchase #7 $206.86   7.192%   $221.7374   $221.74   $221.75   $221.70  
  7 purchase totals = $981.20       $1,053.5085   $1,053.51   $1,053.50   $1,053.40