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 $241.74   11.271%   $268.9865   $268.99   $269.00   $269.00  
  Purchase #2 $39.79   13.622%   $45.2102   $45.21   $45.20   $45.20  
  Purchase #3 $44.28   9.609%   $48.5349   $48.53   $48.55   $48.50  
  Purchase #4 $207.66   10.221%   $228.8849   $228.88   $228.90   $228.90  
  Purchase #5 $216.32   13.109%   $244.6774   $244.68   $244.70   $244.70  
  Purchase #6 $239.25   8.632%   $259.9021   $259.90   $259.90   $259.90  
  Purchase #7 $218.25   5.389%   $230.0115   $230.01   $230.00   $230.00  
  7 purchase totals = $1,207.29       $1,326.2075   $1,326.20   $1,326.25   $1,326.20