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 $208.48   11.746%   $232.9681   $232.97   $232.95   $233.00  
  Purchase #2 $19.60   8.602%   $21.286   $21.29   $21.30   $21.30  
  Purchase #3 $122.72   7.865%   $132.3719   $132.37   $132.35   $132.40  
  Purchase #4 $224.29   12.135%   $251.5076   $251.51   $251.50   $251.50  
  Purchase #5 $59.83   11.425%   $66.6656   $66.67   $66.65   $66.70  
  Purchase #6 $136.58   4.549%   $142.793   $142.79   $142.80   $142.80  
  Purchase #7 $80.67   7.746%   $86.9187   $86.92   $86.90   $86.90  
  7 purchase totals = $852.17       $934.5109   $934.52   $934.45   $934.60