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 $167.52   9.365%   $183.2082   $183.21   $183.20   $183.20  
  Purchase #2 $184.41   5.385%   $194.3405   $194.34   $194.35   $194.30  
  Purchase #3 $77.70   4.108%   $80.8919   $80.89   $80.90   $80.90  
  Purchase #4 $125.51   7.283%   $134.6509   $134.65   $134.65   $134.70  
  Purchase #5 $106.37   4.830%   $111.5077   $111.51   $111.50   $111.50  
  Purchase #6 $81.57   13.723%   $92.7639   $92.76   $92.75   $92.80  
  Purchase #7 $216.63   4.610%   $226.6166   $226.62   $226.60   $226.60  
  7 purchase totals = $959.71       $1,023.9797   $1,023.98   $1,023.95   $1,024.00