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 $169.78   8.327%   $183.9176   $183.92   $183.90   $183.90  
  Purchase #2 $234.76   9.625%   $257.3557   $257.36   $257.35   $257.40  
  Purchase #3 $58.95   11.501%   $65.7298   $65.73   $65.75   $65.70  
  Purchase #4 $239.65   3.421%   $247.8484   $247.85   $247.85   $247.80  
  Purchase #5 $247.59   11.590%   $276.2857   $276.29   $276.30   $276.30  
  Purchase #6 $48.40   13.296%   $54.8353   $54.84   $54.85   $54.80  
  Purchase #7 $8.84   9.651%   $9.6931   $9.69   $9.70   $9.70  
  7 purchase totals = $1,007.97       $1,095.6656   $1,095.68   $1,095.70   $1,095.60