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 $21.35   5.107%   $22.4403   $22.44   $22.45   $22.40  
  Purchase #2 $160.47   4.143%   $167.1183   $167.12   $167.10   $167.10  
  Purchase #3 $109.42   12.490%   $123.0866   $123.09   $123.10   $123.10  
  Purchase #4 $128.35   4.601%   $134.2554   $134.26   $134.25   $134.30  
  Purchase #5 $39.33   3.377%   $40.6582   $40.66   $40.65   $40.70  
  Purchase #6 $76.30   13.728%   $86.7745   $86.77   $86.75   $86.80  
  Purchase #7 $151.78   6.419%   $161.5228   $161.52   $161.50   $161.50  
  7 purchase totals = $687.00       $735.8561   $735.86   $735.80   $735.90