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 $84.82   10.766%   $93.9517   $93.95   $93.95   $94.00  
  Purchase #2 $47.39   11.788%   $52.9763   $52.98   $53.00   $53.00  
  Purchase #3 $155.33   13.540%   $176.3617   $176.36   $176.35   $176.40  
  Purchase #4 $237.50   13.208%   $268.869   $268.87   $268.85   $268.90  
  Purchase #5 $187.96   10.112%   $206.9665   $206.97   $206.95   $207.00  
  Purchase #6 $42.74   10.440%   $47.2021   $47.20   $47.20   $47.20  
  Purchase #7 $145.93   4.469%   $152.4516   $152.45   $152.45   $152.50  
  7 purchase totals = $901.67       $998.7789   $998.78   $998.75   $999.00