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 $194.91   4.432%   $203.5484   $203.55   $203.55   $203.50  
  Purchase #2 $224.71   13.505%   $255.0571   $255.06   $255.05   $255.10  
  Purchase #3 $43.85   12.294%   $49.2409   $49.24   $49.25   $49.20  
  Purchase #4 $228.65   8.465%   $248.0052   $248.01   $248.00   $248.00  
  Purchase #5 $207.71   11.681%   $231.9726   $231.97   $231.95   $232.00  
  Purchase #6 $173.85   11.415%   $193.695   $193.70   $193.70   $193.70  
  Purchase #7 $132.96   11.868%   $148.7397   $148.74   $148.75   $148.70  
  7 purchase totals = $1,206.64       $1,330.2589   $1,330.27   $1,330.25   $1,330.20