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 $204.48   13.461%   $232.0051   $232.01   $232.00   $232.00  
  Purchase #2 $249.45   5.406%   $262.9353   $262.94   $262.95   $262.90  
  Purchase #3 $167.95   12.780%   $189.414   $189.41   $189.40   $189.40  
  Purchase #4 $77.66   9.749%   $85.2311   $85.23   $85.25   $85.20  
  Purchase #5 $222.31   4.789%   $232.9564   $232.96   $232.95   $233.00  
  Purchase #6 $63.38   3.529%   $65.6167   $65.62   $65.60   $65.60  
  Purchase #7 $233.64   10.648%   $258.518   $258.52   $258.50   $258.50  
  7 purchase totals = $1,218.87       $1,326.6766   $1,326.69   $1,326.65   $1,326.60