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 $177.79   8.841%   $193.5084   $193.51   $193.50   $193.50  
  Purchase #2 $52.28   4.542%   $54.6546   $54.65   $54.65   $54.70  
  Purchase #3 $73.80   5.528%   $77.8797   $77.88   $77.90   $77.90  
  Purchase #4 $232.67   6.401%   $247.5632   $247.56   $247.55   $247.60  
  Purchase #5 $151.98   8.485%   $164.8755   $164.88   $164.90   $164.90  
  Purchase #6 $235.91   3.714%   $244.6717   $244.67   $244.65   $244.70  
  Purchase #7 $61.56   6.819%   $65.7578   $65.76   $65.75   $65.80  
  7 purchase totals = $985.99       $1,048.9109   $1,048.91   $1,048.90   $1,049.10