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 $49.65   8.624%   $53.9318   $53.93   $53.95   $53.90  
  Purchase #2 $134.82   6.284%   $143.2921   $143.29   $143.30   $143.30  
  Purchase #3 $94.84   10.501%   $104.7991   $104.80   $104.80   $104.80  
  Purchase #4 $237.89   13.231%   $269.3652   $269.37   $269.35   $269.40  
  Purchase #5 $212.28   7.316%   $227.8104   $227.81   $227.80   $227.80  
  Purchase #6 $177.53   11.561%   $198.0542   $198.05   $198.05   $198.10  
  Purchase #7 $24.30   8.730%   $26.4214   $26.42   $26.40   $26.40  
  7 purchase totals = $931.31       $1,023.6742   $1,023.67   $1,023.65   $1,023.70