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 $10.67   6.257%   $11.3376   $11.34   $11.35   $11.30  
  Purchase #2 $75.75   11.613%   $84.5468   $84.55   $84.55   $84.50  
  Purchase #3 $42.48   10.706%   $47.0279   $47.03   $47.05   $47.00  
  Purchase #4 $240.25   12.690%   $270.7377   $270.74   $270.75   $270.70  
  Purchase #5 $70.36   3.493%   $72.8177   $72.82   $72.80   $72.80  
  Purchase #6 $240.34   7.262%   $257.7935   $257.79   $257.80   $257.80  
  Purchase #7 $203.86   13.655%   $231.6971   $231.70   $231.70   $231.70  
  7 purchase totals = $883.71       $975.9583   $975.97   $976.00   $975.80