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 $84.69   10.340%   $93.4469   $93.45   $93.45   $93.40  
  Purchase #2 $205.99   10.313%   $227.2337   $227.23   $227.25   $227.20  
  Purchase #3 $64.90   7.369%   $69.6825   $69.68   $69.70   $69.70  
  Purchase #4 $110.51   10.607%   $122.2318   $122.23   $122.25   $122.20  
  Purchase #5 $180.79   8.686%   $196.4934   $196.49   $196.50   $196.50  
  Purchase #6 $234.33   3.616%   $242.8034   $242.80   $242.80   $242.80  
  Purchase #7 $20.94   5.260%   $22.0414   $22.04   $22.05   $22.00  
  7 purchase totals = $902.15       $973.9331   $973.92   $974.00   $973.80