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 $247.75   8.646%   $269.1705   $269.17   $269.15   $269.20  
  Purchase #2 $82.48   7.355%   $88.5464   $88.55   $88.55   $88.50  
  Purchase #3 $138.77   5.678%   $146.6494   $146.65   $146.65   $146.60  
  Purchase #4 $139.56   4.327%   $145.5988   $145.60   $145.60   $145.60  
  Purchase #5 $119.60   13.666%   $135.9445   $135.94   $135.95   $135.90  
  Purchase #6 $238.25   12.217%   $267.357   $267.36   $267.35   $267.40  
  Purchase #7 $170.63   7.736%   $183.8299   $183.83   $183.85   $183.80  
  7 purchase totals = $1,137.04       $1,237.0965   $1,237.10   $1,237.10   $1,237.00