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 $118.35   13.264%   $134.0479   $134.05   $134.05   $134.00  
  Purchase #2 $206.59   12.631%   $232.6844   $232.68   $232.70   $232.70  
  Purchase #3 $51.48   8.321%   $55.7637   $55.76   $55.75   $55.80  
  Purchase #4 $183.72   6.632%   $195.9043   $195.90   $195.90   $195.90  
  Purchase #5 $190.68   10.794%   $211.262   $211.26   $211.25   $211.30  
  Purchase #6 $235.70   4.569%   $246.4691   $246.47   $246.45   $246.50  
  Purchase #7 $207.91   11.463%   $231.7427   $231.74   $231.75   $231.70  
  7 purchase totals = $1,194.43       $1,307.8741   $1,307.86   $1,307.85   $1,307.90