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 $68.99   6.268%   $73.3143   $73.31   $73.30   $73.30  
  Purchase #2 $80.52   7.177%   $86.2989   $86.30   $86.30   $86.30  
  Purchase #3 $230.30   10.103%   $253.5672   $253.57   $253.55   $253.60  
  Purchase #4 $99.64   5.722%   $105.3414   $105.34   $105.35   $105.30  
  Purchase #5 $93.98   12.803%   $106.0123   $106.01   $106.00   $106.00  
  Purchase #6 $221.45   7.676%   $238.4485   $238.45   $238.45   $238.40  
  Purchase #7 $125.74   7.343%   $134.9731   $134.97   $134.95   $135.00  
  7 purchase totals = $920.62       $997.9557   $997.95   $997.90   $997.90