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 $149.85   9.523%   $164.1202   $164.12   $164.10   $164.10  
  Purchase #2 $35.37   4.379%   $36.9189   $36.92   $36.90   $36.90  
  Purchase #3 $177.53   9.108%   $193.6994   $193.70   $193.70   $193.70  
  Purchase #4 $14.86   13.382%   $16.8486   $16.85   $16.85   $16.80  
  Purchase #5 $177.26   5.809%   $187.557   $187.56   $187.55   $187.60  
  Purchase #6 $191.74   5.640%   $202.5541   $202.55   $202.55   $202.60  
  Purchase #7 $58.96   5.147%   $61.9947   $61.99   $62.00   $62.00  
  7 purchase totals = $805.57       $863.6929   $863.69   $863.65   $863.70