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 $183.29   12.764%   $206.6851   $206.69   $206.70   $206.70  
  Purchase #2 $69.96   11.754%   $78.1831   $78.18   $78.20   $78.20  
  Purchase #3 $179.38   4.164%   $186.8494   $186.85   $186.85   $186.80  
  Purchase #4 $231.77   6.676%   $247.243   $247.24   $247.25   $247.20  
  Purchase #5 $175.28   8.597%   $190.3488   $190.35   $190.35   $190.30  
  Purchase #6 $194.48   12.375%   $218.5469   $218.55   $218.55   $218.50  
  Purchase #7 $61.89   5.654%   $65.3893   $65.39   $65.40   $65.40  
  7 purchase totals = $1,096.05       $1,193.2456   $1,193.25   $1,193.30   $1,193.10