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 $54.75   12.682%   $61.6934   $61.69   $61.70   $61.70  
  Purchase #2 $11.94   11.798%   $13.3487   $13.35   $13.35   $13.30  
  Purchase #3 $202.83   8.294%   $219.6527   $219.65   $219.65   $219.70  
  Purchase #4 $168.68   7.751%   $181.7544   $181.75   $181.75   $181.80  
  Purchase #5 $179.85   7.228%   $192.8496   $192.85   $192.85   $192.80  
  Purchase #6 $57.91   4.676%   $60.6179   $60.62   $60.60   $60.60  
  Purchase #7 $31.40   13.774%   $35.725   $35.73   $35.75   $35.70  
  7 purchase totals = $707.36       $765.6417   $765.64   $765.65   $765.60