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 $91.82   5.867%   $97.2071   $97.21   $97.20   $97.20  
  Purchase #2 $231.96   4.612%   $242.658   $242.66   $242.65   $242.70  
  Purchase #3 $237.57   8.425%   $257.5853   $257.59   $257.60   $257.60  
  Purchase #4 $54.61   7.579%   $58.7489   $58.75   $58.75   $58.70  
  Purchase #5 $51.52   6.795%   $55.0208   $55.02   $55.00   $55.00  
  Purchase #6 $49.54   7.705%   $53.3571   $53.36   $53.35   $53.40  
  Purchase #7 $54.72   10.114%   $60.2544   $60.25   $60.25   $60.30  
  7 purchase totals = $771.74       $824.8316   $824.84   $824.80   $824.90