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 $207.75   12.703%   $234.1405   $234.14   $234.15   $234.10  
  Purchase #2 $66.32   8.340%   $71.8511   $71.85   $71.85   $71.90  
  Purchase #3 $239.43   10.325%   $264.1511   $264.15   $264.15   $264.20  
  Purchase #4 $184.73   9.155%   $201.642   $201.64   $201.65   $201.60  
  Purchase #5 $20.72   12.358%   $23.2806   $23.28   $23.30   $23.30  
  Purchase #6 $83.30   10.151%   $91.7558   $91.76   $91.75   $91.80  
  Purchase #7 $220.52   6.809%   $235.5352   $235.54   $235.55   $235.50  
  7 purchase totals = $1,022.77       $1,122.3563   $1,122.36   $1,122.40   $1,122.40