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 $88.48   5.745%   $93.5632   $93.56   $93.55   $93.60  
  Purchase #2 $72.90   6.586%   $77.7012   $77.70   $77.70   $77.70  
  Purchase #3 $167.72   9.356%   $183.4119   $183.41   $183.40   $183.40  
  Purchase #4 $247.53   4.271%   $258.102   $258.10   $258.10   $258.10  
  Purchase #5 $161.59   11.798%   $180.6544   $180.65   $180.65   $180.70  
  Purchase #6 $195.71   4.537%   $204.5894   $204.59   $204.60   $204.60  
  Purchase #7 $235.29   8.773%   $255.932   $255.93   $255.95   $255.90  
  7 purchase totals = $1,169.22       $1,253.9541   $1,253.94   $1,253.95   $1,254.00