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 $198.97   11.601%   $222.0525   $222.05   $222.05   $222.10  
  Purchase #2 $55.86   12.773%   $62.995   $63.00   $63.00   $63.00  
  Purchase #3 $118.99   12.596%   $133.978   $133.98   $134.00   $134.00  
  Purchase #4 $71.57   5.551%   $75.5429   $75.54   $75.55   $75.50  
  Purchase #5 $196.26   3.831%   $203.7787   $203.78   $203.80   $203.80  
  Purchase #6 $237.31   12.675%   $267.389   $267.39   $267.40   $267.40  
  Purchase #7 $186.29   7.378%   $200.0345   $200.03   $200.05   $200.00  
  7 purchase totals = $1,065.25       $1,165.7706   $1,165.77   $1,165.85   $1,165.80