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 $228.52   11.586%   $254.9963   $255.00   $255.00   $255.00  
  Purchase #2 $73.64   13.113%   $83.2964   $83.30   $83.30   $83.30  
  Purchase #3 $183.63   9.829%   $201.679   $201.68   $201.70   $201.70  
  Purchase #4 $97.35   8.870%   $105.9849   $105.98   $106.00   $106.00  
  Purchase #5 $192.72   13.397%   $218.5387   $218.54   $218.55   $218.50  
  Purchase #6 $231.58   8.707%   $251.7437   $251.74   $251.75   $251.70  
  Purchase #7 $213.43   7.846%   $230.1757   $230.18   $230.20   $230.20  
  7 purchase totals = $1,220.87       $1,346.4147   $1,346.42   $1,346.50   $1,346.40