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 $60.48   5.801%   $63.9884   $63.99   $64.00   $64.00  
  Purchase #2 $91.70   4.695%   $96.0053   $96.01   $96.00   $96.00  
  Purchase #3 $116.74   12.309%   $131.1095   $131.11   $131.10   $131.10  
  Purchase #4 $127.35   6.214%   $135.2635   $135.26   $135.25   $135.30  
  Purchase #5 $29.41   10.857%   $32.603   $32.60   $32.60   $32.60  
  Purchase #6 $221.40   6.600%   $236.0124   $236.01   $236.00   $236.00  
  Purchase #7 $204.46   10.358%   $225.638   $225.64   $225.65   $225.60  
  7 purchase totals = $851.54       $920.6201   $920.62   $920.60   $920.60