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 $65.55   12.251%   $73.5805   $73.58   $73.60   $73.60  
  Purchase #2 $200.32   10.190%   $220.7326   $220.73   $220.75   $220.70  
  Purchase #3 $22.79   4.771%   $23.8773   $23.88   $23.90   $23.90  
  Purchase #4 $97.64   10.281%   $107.6784   $107.68   $107.70   $107.70  
  Purchase #5 $79.82   13.683%   $90.7418   $90.74   $90.75   $90.70  
  Purchase #6 $173.75   3.425%   $179.7009   $179.70   $179.70   $179.70  
  Purchase #7 $92.90   9.501%   $101.7264   $101.73   $101.75   $101.70  
  7 purchase totals = $732.77       $798.0379   $798.04   $798.15   $798.00