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 $64.67   11.108%   $71.8535   $71.85   $71.85   $71.90  
  Purchase #2 $166.77   3.319%   $172.3051   $172.31   $172.30   $172.30  
  Purchase #3 $6.64   7.313%   $7.1256   $7.13   $7.15   $7.10  
  Purchase #4 $28.79   13.431%   $32.6568   $32.66   $32.65   $32.70  
  Purchase #5 $168.39   7.523%   $181.058   $181.06   $181.05   $181.10  
  Purchase #6 $239.95   9.764%   $263.3787   $263.38   $263.40   $263.40  
  Purchase #7 $87.42   8.723%   $95.0456   $95.05   $95.05   $95.00  
  7 purchase totals = $762.63       $823.4233   $823.44   $823.45   $823.50