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 $56.82   4.442%   $59.3439   $59.34   $59.35   $59.30  
  Purchase #2 $134.77   4.113%   $140.3131   $140.31   $140.30   $140.30  
  Purchase #3 $133.53   4.593%   $139.663   $139.66   $139.65   $139.70  
  Purchase #4 $60.45   8.759%   $65.7448   $65.74   $65.75   $65.70  
  Purchase #5 $114.25   5.697%   $120.7588   $120.76   $120.75   $120.80  
  Purchase #6 $187.36   12.519%   $210.8156   $210.82   $210.80   $210.80  
  Purchase #7 $207.35   7.740%   $223.3989   $223.40   $223.40   $223.40  
  7 purchase totals = $894.53       $960.0381   $960.03   $960.00   $960.00