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 $141.37   10.717%   $156.5206   $156.52   $156.50   $156.50  
  Purchase #2 $50.75   11.579%   $56.6263   $56.63   $56.65   $56.60  
  Purchase #3 $130.63   8.832%   $142.1672   $142.17   $142.15   $142.20  
  Purchase #4 $82.74   8.842%   $90.0559   $90.06   $90.05   $90.10  
  Purchase #5 $192.68   10.135%   $212.2081   $212.21   $212.20   $212.20  
  Purchase #6 $222.50   3.841%   $231.0462   $231.05   $231.05   $231.00  
  Purchase #7 $59.40   10.119%   $65.4107   $65.41   $65.40   $65.40  
  7 purchase totals = $880.07       $954.0350   $954.05   $954.00   $954.00