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 $65.62   6.593%   $69.9463   $69.95   $69.95   $69.90  
  Purchase #2 $226.95   3.372%   $234.6028   $234.60   $234.60   $234.60  
  Purchase #3 $90.41   3.769%   $93.8176   $93.82   $93.80   $93.80  
  Purchase #4 $204.39   12.641%   $230.2269   $230.23   $230.25   $230.20  
  Purchase #5 $206.37   4.164%   $214.9632   $214.96   $214.95   $215.00  
  Purchase #6 $200.98   6.505%   $214.0537   $214.05   $214.05   $214.10  
  Purchase #7 $204.82   5.534%   $216.1547   $216.15   $216.15   $216.20  
  7 purchase totals = $1,199.54       $1,273.7652   $1,273.76   $1,273.75   $1,273.80