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 $62.65   5.118%   $65.8564   $65.86   $65.85   $65.90  
  Purchase #2 $46.85   6.837%   $50.0531   $50.05   $50.05   $50.10  
  Purchase #3 $190.98   11.193%   $212.3564   $212.36   $212.35   $212.40  
  Purchase #4 $161.85   9.687%   $177.5284   $177.53   $177.55   $177.50  
  Purchase #5 $57.53   10.252%   $63.428   $63.43   $63.45   $63.40  
  Purchase #6 $85.53   8.731%   $92.9976   $93.00   $93.00   $93.00  
  Purchase #7 $124.66   10.444%   $137.6795   $137.68   $137.70   $137.70  
  7 purchase totals = $730.05       $799.8994   $799.91   $799.95   $800.00