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 $166.78   5.613%   $176.1414   $176.14   $176.15   $176.10  
  Purchase #2 $68.25   7.830%   $73.594   $73.59   $73.60   $73.60  
  Purchase #3 $197.87   7.466%   $212.643   $212.64   $212.65   $212.60  
  Purchase #4 $43.41   7.410%   $46.6267   $46.63   $46.65   $46.60  
  Purchase #5 $133.96   11.213%   $148.9809   $148.98   $149.00   $149.00  
  Purchase #6 $250.38   10.448%   $276.5397   $276.54   $276.55   $276.50  
  Purchase #7 $77.40   10.154%   $85.2592   $85.26   $85.25   $85.30  
  7 purchase totals = $938.05       $1,019.7849   $1,019.78   $1,019.85   $1,019.70