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 $58.50   7.731%   $63.0226   $63.02   $63.00   $63.00  
  Purchase #2 $230.96   3.373%   $238.7503   $238.75   $238.75   $238.80  
  Purchase #3 $228.44   9.728%   $250.6626   $250.66   $250.65   $250.70  
  Purchase #4 $97.96   4.723%   $102.5867   $102.59   $102.60   $102.60  
  Purchase #5 $232.63   13.484%   $263.9978   $264.00   $264.00   $264.00  
  Purchase #6 $82.57   11.406%   $91.9879   $91.99   $92.00   $92.00  
  Purchase #7 $57.60   9.784%   $63.2356   $63.24   $63.25   $63.20  
  7 purchase totals = $988.66       $1,074.2435   $1,074.25   $1,074.25   $1,074.30