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 $218.72   8.472%   $237.25   $237.25   $237.25   $237.30  
  Purchase #2 $44.58   7.817%   $48.0648   $48.06   $48.05   $48.10  
  Purchase #3 $237.41   5.576%   $250.648   $250.65   $250.65   $250.60  
  Purchase #4 $66.99   7.202%   $71.8146   $71.81   $71.80   $71.80  
  Purchase #5 $214.52   10.325%   $236.6692   $236.67   $236.65   $236.70  
  Purchase #6 $49.50   11.279%   $55.0831   $55.08   $55.10   $55.10  
  Purchase #7 $146.34   3.368%   $151.2687   $151.27   $151.25   $151.30  
  7 purchase totals = $978.06       $1,050.7984   $1,050.79   $1,050.75   $1,050.90