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 $49.66   7.574%   $53.4212   $53.42   $53.40   $53.40  
  Purchase #2 $192.25   11.259%   $213.8954   $213.90   $213.90   $213.90  
  Purchase #3 $123.45   6.137%   $131.0261   $131.03   $131.05   $131.00  
  Purchase #4 $56.48   7.625%   $60.7866   $60.79   $60.80   $60.80  
  Purchase #5 $166.31   5.648%   $175.7032   $175.70   $175.70   $175.70  
  Purchase #6 $220.95   11.107%   $245.4909   $245.49   $245.50   $245.50  
  Purchase #7 $49.65   10.747%   $54.9859   $54.99   $55.00   $55.00  
  7 purchase totals = $858.75       $935.3093   $935.32   $935.35   $935.30