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 $63.88   4.348%   $66.6575   $66.66   $66.65   $66.70  
  Purchase #2 $201.34   3.464%   $208.3144   $208.31   $208.30   $208.30  
  Purchase #3 $99.38   7.644%   $106.9766   $106.98   $107.00   $107.00  
  Purchase #4 $213.85   12.539%   $240.6647   $240.66   $240.65   $240.70  
  Purchase #5 $227.50   6.855%   $243.0951   $243.10   $243.10   $243.10  
  Purchase #6 $211.98   8.224%   $229.4132   $229.41   $229.40   $229.40  
  Purchase #7 $200.52   3.671%   $207.8811   $207.88   $207.90   $207.90  
  7 purchase totals = $1,218.45       $1,303.0026   $1,303.00   $1,303.00   $1,303.10