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 $93.51   13.174%   $105.829   $105.83   $105.85   $105.80  
  Purchase #2 $124.70   10.174%   $137.387   $137.39   $137.40   $137.40  
  Purchase #3 $113.95   4.128%   $118.6539   $118.65   $118.65   $118.70  
  Purchase #4 $57.86   3.617%   $59.9528   $59.95   $59.95   $60.00  
  Purchase #5 $242.98   6.869%   $259.6703   $259.67   $259.65   $259.70  
  Purchase #6 $102.62   6.365%   $109.1518   $109.15   $109.15   $109.20  
  Purchase #7 $124.56   6.809%   $133.0413   $133.04   $133.05   $133.00  
  7 purchase totals = $860.18       $923.6861   $923.68   $923.70   $923.80