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 $184.92   5.269%   $194.6634   $194.66   $194.65   $194.70  
  Purchase #2 $226.91   9.178%   $247.7358   $247.74   $247.75   $247.70  
  Purchase #3 $30.52   13.815%   $34.7363   $34.74   $34.75   $34.70  
  Purchase #4 $121.52   4.748%   $127.2898   $127.29   $127.30   $127.30  
  Purchase #5 $132.80   7.563%   $142.8437   $142.84   $142.85   $142.80  
  Purchase #6 $206.62   4.157%   $215.2092   $215.21   $215.20   $215.20  
  Purchase #7 $241.61   13.176%   $273.4445   $273.44   $273.45   $273.40  
  7 purchase totals = $1,144.90       $1,235.9227   $1,235.92   $1,235.95   $1,235.80