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 $69.54   5.370%   $73.2743   $73.27   $73.25   $73.30  
  Purchase #2 $88.25   8.334%   $95.6048   $95.60   $95.60   $95.60  
  Purchase #3 $11.50   5.587%   $12.1425   $12.14   $12.15   $12.10  
  Purchase #4 $25.40   8.476%   $27.5529   $27.55   $27.55   $27.60  
  Purchase #5 $215.44   10.713%   $238.5201   $238.52   $238.50   $238.50  
  Purchase #6 $197.52   13.852%   $224.8805   $224.88   $224.90   $224.90  
  Purchase #7 $193.87   13.249%   $219.5558   $219.56   $219.55   $219.60  
  7 purchase totals = $801.52       $891.5309   $891.52   $891.50   $891.60