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 $106.70   6.732%   $113.883   $113.88   $113.90   $113.90  
  Purchase #2 $10.58   10.444%   $11.685   $11.69   $11.70   $11.70  
  Purchase #3 $212.92   10.841%   $236.0027   $236.00   $236.00   $236.00  
  Purchase #4 $82.88   6.822%   $88.5341   $88.53   $88.55   $88.50  
  Purchase #5 $33.92   3.666%   $35.1635   $35.16   $35.15   $35.20  
  Purchase #6 $126.92   11.615%   $141.6618   $141.66   $141.65   $141.70  
  Purchase #7 $235.33   5.242%   $247.666   $247.67   $247.65   $247.70  
  7 purchase totals = $809.25       $874.5961   $874.59   $874.60   $874.70