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 $23.76   3.352%   $24.5564   $24.56   $24.55   $24.60  
  Purchase #2 $235.28   5.373%   $247.9216   $247.92   $247.90   $247.90  
  Purchase #3 $211.87   11.554%   $236.3495   $236.35   $236.35   $236.30  
  Purchase #4 $58.40   4.300%   $60.9112   $60.91   $60.90   $60.90  
  Purchase #5 $38.37   6.589%   $40.8982   $40.90   $40.90   $40.90  
  Purchase #6 $121.98   4.337%   $127.2703   $127.27   $127.25   $127.30  
  Purchase #7 $205.98   5.281%   $216.8578   $216.86   $216.85   $216.90  
  7 purchase totals = $895.64       $954.7650   $954.77   $954.70   $954.80