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 $60.90   8.637%   $66.1599   $66.16   $66.15   $66.20  
  Purchase #2 $156.41   11.202%   $173.931   $173.93   $173.95   $173.90  
  Purchase #3 $148.81   4.544%   $155.5719   $155.57   $155.55   $155.60  
  Purchase #4 $168.68   13.814%   $191.9815   $191.98   $192.00   $192.00  
  Purchase #5 $243.60   12.346%   $273.6749   $273.67   $273.65   $273.70  
  Purchase #6 $97.60   7.200%   $104.6272   $104.63   $104.65   $104.60  
  Purchase #7 $157.86   11.262%   $175.6382   $175.64   $175.65   $175.60  
  7 purchase totals = $1,033.86       $1,141.5846   $1,141.58   $1,141.60   $1,141.60