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 $50.37   4.863%   $52.8195   $52.82   $52.80   $52.80  
  Purchase #2 $72.49   11.141%   $80.5661   $80.57   $80.55   $80.60  
  Purchase #3 $55.29   9.358%   $60.464   $60.46   $60.45   $60.50  
  Purchase #4 $233.95   3.350%   $241.7873   $241.79   $241.80   $241.80  
  Purchase #5 $219.29   7.809%   $236.4144   $236.41   $236.40   $236.40  
  Purchase #6 $189.86   11.715%   $212.1021   $212.10   $212.10   $212.10  
  Purchase #7 $65.42   4.290%   $68.2265   $68.23   $68.25   $68.20  
  7 purchase totals = $886.67       $952.3799   $952.38   $952.35   $952.40