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 $182.58   13.363%   $206.9782   $206.98   $207.00   $207.00  
  Purchase #2 $102.71   7.127%   $110.0301   $110.03   $110.05   $110.00  
  Purchase #3 $161.52   11.223%   $179.6474   $179.65   $179.65   $179.60  
  Purchase #4 $228.40   8.360%   $247.4942   $247.49   $247.50   $247.50  
  Purchase #5 $161.28   8.187%   $174.484   $174.48   $174.50   $174.50  
  Purchase #6 $186.92   4.663%   $195.6361   $195.64   $195.65   $195.60  
  Purchase #7 $132.81   8.703%   $144.3685   $144.37   $144.35   $144.40  
  7 purchase totals = $1,156.22       $1,258.6385   $1,258.64   $1,258.70   $1,258.60