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 $133.95   10.263%   $147.6973   $147.70   $147.70   $147.70  
  Purchase #2 $118.97   13.232%   $134.7121   $134.71   $134.70   $134.70  
  Purchase #3 $222.79   8.268%   $241.2103   $241.21   $241.20   $241.20  
  Purchase #4 $236.52   4.750%   $247.7547   $247.75   $247.75   $247.80  
  Purchase #5 $65.70   5.734%   $69.4672   $69.47   $69.45   $69.50  
  Purchase #6 $240.95   5.343%   $253.824   $253.82   $253.80   $253.80  
  Purchase #7 $236.27   7.619%   $254.2714   $254.27   $254.25   $254.30  
  7 purchase totals = $1,255.15       $1,348.9370   $1,348.93   $1,348.85   $1,349.00