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 $203.76   11.260%   $226.7034   $226.70   $226.70   $226.70  
  Purchase #2 $112.74   6.384%   $119.9373   $119.94   $119.95   $119.90  
  Purchase #3 $33.85   5.213%   $35.6146   $35.61   $35.60   $35.60  
  Purchase #4 $146.65   10.777%   $162.4545   $162.45   $162.45   $162.50  
  Purchase #5 $67.70   11.252%   $75.3176   $75.32   $75.30   $75.30  
  Purchase #6 $111.48   8.566%   $121.0294   $121.03   $121.05   $121.00  
  Purchase #7 $206.66   10.776%   $228.9297   $228.93   $228.95   $228.90  
  7 purchase totals = $882.84       $969.9865   $969.98   $970.00   $969.90