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 $188.99   8.261%   $204.6025   $204.60   $204.60   $204.60  
  Purchase #2 $71.61   7.220%   $76.7802   $76.78   $76.80   $76.80  
  Purchase #3 $117.46   10.408%   $129.6852   $129.69   $129.70   $129.70  
  Purchase #4 $109.64   3.801%   $113.8074   $113.81   $113.80   $113.80  
  Purchase #5 $123.82   10.840%   $137.2421   $137.24   $137.25   $137.20  
  Purchase #6 $146.76   4.479%   $153.3334   $153.33   $153.35   $153.30  
  Purchase #7 $141.37   10.385%   $156.0513   $156.05   $156.05   $156.10  
  7 purchase totals = $899.65       $971.5021   $971.50   $971.55   $971.50