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 $87.55   8.795%   $95.25   $95.25   $95.25   $95.30  
  Purchase #2 $73.86   10.437%   $81.5688   $81.57   $81.55   $81.60  
  Purchase #3 $137.64   7.556%   $148.0401   $148.04   $148.05   $148.00  
  Purchase #4 $154.29   11.790%   $172.4808   $172.48   $172.50   $172.50  
  Purchase #5 $245.68   12.769%   $277.0509   $277.05   $277.05   $277.10  
  Purchase #6 $194.58   4.659%   $203.6455   $203.65   $203.65   $203.60  
  Purchase #7 $174.76   10.818%   $193.6655   $193.67   $193.65   $193.70  
  7 purchase totals = $1,068.36       $1,171.7016   $1,171.71   $1,171.70   $1,171.80