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 $247.66   6.309%   $263.2849   $263.28   $263.30   $263.30  
  Purchase #2 $81.90   13.573%   $93.0163   $93.02   $93.00   $93.00  
  Purchase #3 $31.97   6.453%   $34.033   $34.03   $34.05   $34.00  
  Purchase #4 $238.84   5.106%   $251.0352   $251.04   $251.05   $251.00  
  Purchase #5 $97.55   10.332%   $107.6289   $107.63   $107.65   $107.60  
  Purchase #6 $129.34   4.872%   $135.6414   $135.64   $135.65   $135.60  
  Purchase #7 $109.88   5.788%   $116.2399   $116.24   $116.25   $116.20  
  7 purchase totals = $937.14       $1,000.8796   $1,000.88   $1,000.95   $1,000.70