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 $87.85   7.396%   $94.3474   $94.35   $94.35   $94.30  
  Purchase #2 $235.74   6.791%   $251.7491   $251.75   $251.75   $251.70  
  Purchase #3 $32.37   3.556%   $33.5211   $33.52   $33.50   $33.50  
  Purchase #4 $137.49   13.641%   $156.245   $156.25   $156.25   $156.20  
  Purchase #5 $73.62   13.524%   $83.5764   $83.58   $83.60   $83.60  
  Purchase #6 $110.49   12.655%   $124.4725   $124.47   $124.45   $124.50  
  Purchase #7 $89.46   11.774%   $99.993   $99.99   $100.00   $100.00  
  7 purchase totals = $767.02       $843.9045   $843.91   $843.90   $843.80