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 $249.55   7.237%   $267.6099   $267.61   $267.60   $267.60  
  Purchase #2 $150.63   6.245%   $160.0368   $160.04   $160.05   $160.00  
  Purchase #3 $208.26   9.354%   $227.7406   $227.74   $227.75   $227.70  
  Purchase #4 $122.48   6.565%   $130.5208   $130.52   $130.50   $130.50  
  Purchase #5 $179.72   13.769%   $204.4656   $204.47   $204.45   $204.50  
  Purchase #6 $54.62   11.785%   $61.057   $61.06   $61.05   $61.10  
  Purchase #7 $59.57   6.379%   $63.37   $63.37   $63.35   $63.40  
  7 purchase totals = $1,024.83       $1,114.8007   $1,114.81   $1,114.75   $1,114.80