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 $146.32   5.624%   $154.549   $154.55   $154.55   $154.50  
  Purchase #2 $241.98   11.235%   $269.1665   $269.17   $269.15   $269.20  
  Purchase #3 $75.77   12.553%   $85.2814   $85.28   $85.30   $85.30  
  Purchase #4 $199.39   4.836%   $209.0325   $209.03   $209.05   $209.00  
  Purchase #5 $250.29   13.411%   $283.8564   $283.86   $283.85   $283.90  
  Purchase #6 $230.61   5.418%   $243.1044   $243.10   $243.10   $243.10  
  Purchase #7 $95.75   5.685%   $101.1934   $101.19   $101.20   $101.20  
  7 purchase totals = $1,240.11       $1,346.1836   $1,346.18   $1,346.20   $1,346.20