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 $206.97   13.871%   $235.6788   $235.68   $235.70   $235.70  
  Purchase #2 $215.95   13.271%   $244.6087   $244.61   $244.60   $244.60  
  Purchase #3 $246.41   9.132%   $268.9122   $268.91   $268.90   $268.90  
  Purchase #4 $47.96   12.284%   $53.8514   $53.85   $53.85   $53.90  
  Purchase #5 $168.96   12.467%   $190.0242   $190.02   $190.00   $190.00  
  Purchase #6 $155.67   6.442%   $165.6983   $165.70   $165.70   $165.70  
  Purchase #7 $81.36   8.515%   $88.2878   $88.29   $88.30   $88.30  
  7 purchase totals = $1,123.28       $1,247.0614   $1,247.06   $1,247.05   $1,247.10