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 $234.61   13.873%   $267.1574   $267.16   $267.15   $267.20  
  Purchase #2 $5.65   5.344%   $5.9519   $5.95   $5.95   $6.00  
  Purchase #3 $11.33   9.563%   $12.4135   $12.41   $12.40   $12.40  
  Purchase #4 $115.61   5.570%   $122.0495   $122.05   $122.05   $122.00  
  Purchase #5 $148.86   7.776%   $160.4354   $160.44   $160.45   $160.40  
  Purchase #6 $179.25   5.453%   $189.0245   $189.02   $189.00   $189.00  
  Purchase #7 $200.88   4.494%   $209.9075   $209.91   $209.90   $209.90  
  7 purchase totals = $896.19       $966.9397   $966.94   $966.90   $966.90