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 $242.87   9.658%   $266.3264   $266.33   $266.35   $266.30  
  Purchase #2 $115.57   5.755%   $122.2211   $122.22   $122.20   $122.20  
  Purchase #3 $41.43   6.381%   $44.0736   $44.07   $44.05   $44.10  
  Purchase #4 $245.54   6.194%   $260.7487   $260.75   $260.75   $260.70  
  Purchase #5 $5.82   10.494%   $6.4308   $6.43   $6.45   $6.40  
  Purchase #6 $58.64   12.508%   $65.9747   $65.97   $65.95   $66.00  
  Purchase #7 $137.72   5.606%   $145.4406   $145.44   $145.45   $145.40  
  7 purchase totals = $847.59       $911.2159   $911.21   $911.20   $911.10