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 $66.64   13.658%   $75.7417   $75.74   $75.75   $75.70  
  Purchase #2 $187.38   8.624%   $203.5397   $203.54   $203.55   $203.50  
  Purchase #3 $239.67   3.344%   $247.6846   $247.68   $247.70   $247.70  
  Purchase #4 $219.75   4.185%   $228.9465   $228.95   $228.95   $228.90  
  Purchase #5 $136.84   3.387%   $141.4748   $141.47   $141.45   $141.50  
  Purchase #6 $60.97   13.450%   $69.1705   $69.17   $69.15   $69.20  
  Purchase #7 $191.70   4.402%   $200.1386   $200.14   $200.15   $200.10  
  7 purchase totals = $1,102.95       $1,166.6964   $1,166.69   $1,166.70   $1,166.60