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 $245.43   10.537%   $271.291   $271.29   $271.30   $271.30  
  Purchase #2 $14.37   6.562%   $15.313   $15.31   $15.30   $15.30  
  Purchase #3 $192.90   8.383%   $209.0708   $209.07   $209.05   $209.10  
  Purchase #4 $26.95   9.488%   $29.507   $29.51   $29.50   $29.50  
  Purchase #5 $20.75   13.339%   $23.5178   $23.52   $23.50   $23.50  
  Purchase #6 $211.70   13.103%   $239.4391   $239.44   $239.45   $239.40  
  Purchase #7 $200.92   12.446%   $225.9265   $225.93   $225.95   $225.90  
  7 purchase totals = $913.02       $1,014.0652   $1,014.07   $1,014.05   $1,014.00