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 $213.78   10.376%   $235.9618   $235.96   $235.95   $236.00  
  Purchase #2 $165.76   8.827%   $180.3916   $180.39   $180.40   $180.40  
  Purchase #3 $226.62   11.715%   $253.1685   $253.17   $253.15   $253.20  
  Purchase #4 $180.42   7.108%   $193.2443   $193.24   $193.25   $193.20  
  Purchase #5 $86.55   11.649%   $96.6322   $96.63   $96.65   $96.60  
  Purchase #6 $244.71   12.385%   $275.0173   $275.02   $275.00   $275.00  
  Purchase #7 $203.35   11.459%   $226.6519   $226.65   $226.65   $226.70  
  7 purchase totals = $1,321.19       $1,461.0676   $1,461.06   $1,461.05   $1,461.10