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 $63.76   6.148%   $67.68   $67.68   $67.70   $67.70  
  Purchase #2 $104.72   12.577%   $117.8906   $117.89   $117.90   $117.90  
  Purchase #3 $74.84   4.140%   $77.9384   $77.94   $77.95   $77.90  
  Purchase #4 $241.70   7.477%   $259.7719   $259.77   $259.75   $259.80  
  Purchase #5 $90.67   6.280%   $96.3641   $96.36   $96.35   $96.40  
  Purchase #6 $68.37   8.427%   $74.1315   $74.13   $74.15   $74.10  
  Purchase #7 $121.42   10.466%   $134.1278   $134.13   $134.15   $134.10  
  7 purchase totals = $765.48       $827.9043   $827.90   $827.95   $827.90