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 $205.88   8.647%   $223.6824   $223.68   $223.70   $223.70  
  Purchase #2 $153.27   8.277%   $165.9562   $165.96   $165.95   $166.00  
  Purchase #3 $26.29   3.869%   $27.3072   $27.31   $27.30   $27.30  
  Purchase #4 $161.39   7.170%   $172.9617   $172.96   $172.95   $173.00  
  Purchase #5 $18.59   7.420%   $19.9694   $19.97   $19.95   $20.00  
  Purchase #6 $242.71   5.287%   $255.5421   $255.54   $255.55   $255.50  
  Purchase #7 $25.93   8.627%   $28.167   $28.17   $28.15   $28.20  
  7 purchase totals = $834.06       $893.5860   $893.59   $893.55   $893.70