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 $64.54   8.751%   $70.1879   $70.19   $70.20   $70.20  
  Purchase #2 $146.42   7.436%   $157.3078   $157.31   $157.30   $157.30  
  Purchase #3 $243.26   7.148%   $260.6482   $260.65   $260.65   $260.60  
  Purchase #4 $10.54   10.761%   $11.6742   $11.67   $11.65   $11.70  
  Purchase #5 $105.74   9.629%   $115.9217   $115.92   $115.90   $115.90  
  Purchase #6 $221.70   9.234%   $242.1718   $242.17   $242.15   $242.20  
  Purchase #7 $35.32   10.563%   $39.0509   $39.05   $39.05   $39.10  
  7 purchase totals = $827.52       $896.9625   $896.96   $896.90   $897.00