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 $228.98   10.571%   $253.1855   $253.19   $253.20   $253.20  
  Purchase #2 $58.40   11.795%   $65.2883   $65.29   $65.30   $65.30  
  Purchase #3 $166.26   3.197%   $171.5753   $171.58   $171.60   $171.60  
  Purchase #4 $203.40   12.326%   $228.4711   $228.47   $228.45   $228.50  
  Purchase #5 $133.58   5.270%   $140.6197   $140.62   $140.60   $140.60  
  Purchase #6 $40.45   7.522%   $43.4926   $43.49   $43.50   $43.50  
  Purchase #7 $97.27   11.409%   $108.3675   $108.37   $108.35   $108.40  
  7 purchase totals = $928.34       $1,011.0000   $1,011.01   $1,011.00   $1,011.10