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 $37.41   11.607%   $41.7522   $41.75   $41.75   $41.80  
  Purchase #2 $56.63   6.485%   $60.3025   $60.30   $60.30   $60.30  
  Purchase #3 $181.66   8.803%   $197.6515   $197.65   $197.65   $197.70  
  Purchase #4 $213.92   5.691%   $226.0942   $226.09   $226.10   $226.10  
  Purchase #5 $49.46   9.721%   $54.268   $54.27   $54.25   $54.30  
  Purchase #6 $224.99   6.229%   $239.0046   $239.00   $239.00   $239.00  
  Purchase #7 $150.29   4.589%   $157.1868   $157.19   $157.20   $157.20  
  7 purchase totals = $914.36       $976.2598   $976.25   $976.25   $976.40