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 $201.50   10.685%   $223.0303   $223.03   $223.05   $223.00  
  Purchase #2 $169.30   10.367%   $186.8513   $186.85   $186.85   $186.90  
  Purchase #3 $52.54   13.833%   $59.8079   $59.81   $59.80   $59.80  
  Purchase #4 $178.55   7.700%   $192.2984   $192.30   $192.30   $192.30  
  Purchase #5 $113.82   3.408%   $117.699   $117.70   $117.70   $117.70  
  Purchase #6 $181.74   7.700%   $195.734   $195.73   $195.75   $195.70  
  Purchase #7 $18.67   4.392%   $19.49   $19.49   $19.50   $19.50  
  7 purchase totals = $916.12       $994.9109   $994.91   $994.95   $994.90