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 $82.79   3.576%   $85.7506   $85.75   $85.75   $85.80  
  Purchase #2 $54.72   5.387%   $57.6678   $57.67   $57.65   $57.70  
  Purchase #3 $215.28   12.765%   $242.7605   $242.76   $242.75   $242.80  
  Purchase #4 $31.52   9.597%   $34.545   $34.55   $34.55   $34.50  
  Purchase #5 $186.52   11.151%   $207.3188   $207.32   $207.30   $207.30  
  Purchase #6 $199.90   3.125%   $206.1469   $206.15   $206.15   $206.10  
  Purchase #7 $144.56   11.280%   $160.8664   $160.87   $160.85   $160.90  
  7 purchase totals = $915.29       $995.0560   $995.07   $995.00   $995.10