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 $32.76   11.432%   $36.5051   $36.51   $36.50   $36.50  
  Purchase #2 $134.69   9.132%   $146.9899   $146.99   $147.00   $147.00  
  Purchase #3 $181.95   10.400%   $200.8728   $200.87   $200.85   $200.90  
  Purchase #4 $49.28   6.425%   $52.4462   $52.45   $52.45   $52.40  
  Purchase #5 $130.32   8.211%   $141.0206   $141.02   $141.00   $141.00  
  Purchase #6 $199.45   8.316%   $216.0363   $216.04   $216.05   $216.00  
  Purchase #7 $202.57   11.511%   $225.8878   $225.89   $225.90   $225.90  
  7 purchase totals = $931.02       $1,019.7587   $1,019.77   $1,019.75   $1,019.70