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 $82.51   11.451%   $91.9582   $91.96   $91.95   $92.00  
  Purchase #2 $155.92   8.173%   $168.6633   $168.66   $168.65   $168.70  
  Purchase #3 $242.59   9.659%   $266.0218   $266.02   $266.00   $266.00  
  Purchase #4 $183.80   5.149%   $193.2639   $193.26   $193.25   $193.30  
  Purchase #5 $80.58   9.207%   $87.999   $88.00   $88.00   $88.00  
  Purchase #6 $104.81   12.794%   $118.2194   $118.22   $118.20   $118.20  
  Purchase #7 $133.79   9.454%   $146.4385   $146.44   $146.45   $146.40  
  7 purchase totals = $984.00       $1,072.5641   $1,072.56   $1,072.50   $1,072.60