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 $228.72   9.124%   $249.5884   $249.59   $249.60   $249.60  
  Purchase #2 $157.80   5.793%   $166.9414   $166.94   $166.95   $166.90  
  Purchase #3 $52.92   12.654%   $59.6165   $59.62   $59.60   $59.60  
  Purchase #4 $229.51   7.578%   $246.9023   $246.90   $246.90   $246.90  
  Purchase #5 $193.36   13.241%   $218.9628   $218.96   $218.95   $219.00  
  Purchase #6 $153.34   5.632%   $161.9761   $161.98   $162.00   $162.00  
  Purchase #7 $155.83   13.755%   $177.2644   $177.26   $177.25   $177.30  
  7 purchase totals = $1,171.48       $1,281.2519   $1,281.25   $1,281.25   $1,281.30