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 $34.69   11.220%   $38.5822   $38.58   $38.60   $38.60  
  Purchase #2 $216.60   12.764%   $244.2468   $244.25   $244.25   $244.20  
  Purchase #3 $199.67   3.557%   $206.7723   $206.77   $206.75   $206.80  
  Purchase #4 $87.50   11.799%   $97.8241   $97.82   $97.80   $97.80  
  Purchase #5 $177.98   12.563%   $200.3396   $200.34   $200.35   $200.30  
  Purchase #6 $54.86   5.206%   $57.716   $57.72   $57.70   $57.70  
  Purchase #7 $58.94   11.184%   $65.5318   $65.53   $65.55   $65.50  
  7 purchase totals = $830.24       $911.0128   $911.01   $911.00   $910.90