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 $177.51   13.582%   $201.6194   $201.62   $201.60   $201.60  
  Purchase #2 $22.44   9.546%   $24.5821   $24.58   $24.60   $24.60  
  Purchase #3 $230.29   7.324%   $247.1564   $247.16   $247.15   $247.20  
  Purchase #4 $55.97   6.671%   $59.7038   $59.70   $59.70   $59.70  
  Purchase #5 $235.81   13.297%   $267.1657   $267.17   $267.15   $267.20  
  Purchase #6 $39.45   7.332%   $42.3425   $42.34   $42.35   $42.30  
  Purchase #7 $6.79   3.697%   $7.041   $7.04   $7.05   $7.00  
  7 purchase totals = $768.26       $849.6109   $849.61   $849.60   $849.60