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 $241.59   11.340%   $268.9863   $268.99   $269.00   $269.00  
  Purchase #2 $19.79   9.413%   $21.6528   $21.65   $21.65   $21.70  
  Purchase #3 $45.34   10.162%   $49.9475   $49.95   $49.95   $49.90  
  Purchase #4 $244.80   3.475%   $253.3068   $253.31   $253.30   $253.30  
  Purchase #5 $176.42   4.258%   $183.932   $183.93   $183.95   $183.90  
  Purchase #6 $171.69   13.107%   $194.1934   $194.19   $194.20   $194.20  
  Purchase #7 $228.86   13.304%   $259.3075   $259.31   $259.30   $259.30  
  7 purchase totals = $1,128.49       $1,231.3263   $1,231.33   $1,231.35   $1,231.30