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 $59.26   8.133%   $64.0796   $64.08   $64.10   $64.10  
  Purchase #2 $10.79   8.534%   $11.7108   $11.71   $11.70   $11.70  
  Purchase #3 $90.79   4.295%   $94.6894   $94.69   $94.70   $94.70  
  Purchase #4 $230.95   13.456%   $262.0266   $262.03   $262.05   $262.00  
  Purchase #5 $197.93   6.166%   $210.1344   $210.13   $210.15   $210.10  
  Purchase #6 $191.93   12.126%   $215.2034   $215.20   $215.20   $215.20  
  Purchase #7 $151.44   13.194%   $171.421   $171.42   $171.40   $171.40  
  7 purchase totals = $933.09       $1,029.2652   $1,029.26   $1,029.30   $1,029.20