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 $232.83   9.318%   $254.5251   $254.53   $254.55   $254.50  
  Purchase #2 $210.98   5.269%   $222.0965   $222.10   $222.10   $222.10  
  Purchase #3 $156.93   4.399%   $163.8334   $163.83   $163.85   $163.80  
  Purchase #4 $221.56   4.250%   $230.9763   $230.98   $231.00   $231.00  
  Purchase #5 $47.66   3.440%   $49.2995   $49.30   $49.30   $49.30  
  Purchase #6 $165.27   12.834%   $186.4808   $186.48   $186.50   $186.50  
  Purchase #7 $142.35   3.288%   $147.0305   $147.03   $147.05   $147.00  
  7 purchase totals = $1,177.58       $1,254.2421   $1,254.25   $1,254.35   $1,254.20