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 $29.69   12.182%   $33.3068   $33.31   $33.30   $33.30  
  Purchase #2 $181.90   12.354%   $204.3719   $204.37   $204.35   $204.40  
  Purchase #3 $72.82   3.314%   $75.2333   $75.23   $75.25   $75.20  
  Purchase #4 $201.86   3.460%   $208.8444   $208.84   $208.85   $208.80  
  Purchase #5 $187.65   12.864%   $211.7893   $211.79   $211.80   $211.80  
  Purchase #6 $39.29   4.617%   $41.104   $41.10   $41.10   $41.10  
  Purchase #7 $171.87   8.719%   $186.8553   $186.86   $186.85   $186.90  
  7 purchase totals = $885.08       $961.5050   $961.50   $961.50   $961.50