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 $48.55   11.349%   $54.0599   $54.06   $54.05   $54.10  
  Purchase #2 $21.51   12.595%   $24.2192   $24.22   $24.20   $24.20  
  Purchase #3 $113.90   5.315%   $119.9538   $119.95   $119.95   $120.00  
  Purchase #4 $162.88   3.831%   $169.1199   $169.12   $169.10   $169.10  
  Purchase #5 $198.68   9.467%   $217.489   $217.49   $217.50   $217.50  
  Purchase #6 $196.89   7.560%   $211.7749   $211.77   $211.75   $211.80  
  Purchase #7 $155.72   6.297%   $165.5257   $165.53   $165.55   $165.50  
  7 purchase totals = $898.13       $962.1424   $962.14   $962.10   $962.20