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 $10.81   7.418%   $11.6119   $11.61   $11.60   $11.60  
  Purchase #2 $183.58   13.219%   $207.8474   $207.85   $207.85   $207.80  
  Purchase #3 $25.59   7.213%   $27.4358   $27.44   $27.45   $27.40  
  Purchase #4 $181.85   10.298%   $200.5769   $200.58   $200.60   $200.60  
  Purchase #5 $229.25   12.182%   $257.1772   $257.18   $257.20   $257.20  
  Purchase #6 $143.55   12.606%   $161.6459   $161.65   $161.65   $161.60  
  Purchase #7 $243.32   3.147%   $250.9773   $250.98   $251.00   $251.00  
  7 purchase totals = $1,017.95       $1,117.2724   $1,117.29   $1,117.35   $1,117.20