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 $149.76   11.501%   $166.9839   $166.98   $167.00   $167.00  
  Purchase #2 $126.90   3.764%   $131.6765   $131.68   $131.70   $131.70  
  Purchase #3 $27.71   3.288%   $28.6211   $28.62   $28.60   $28.60  
  Purchase #4 $185.30   10.822%   $205.3532   $205.35   $205.35   $205.40  
  Purchase #5 $47.74   9.202%   $52.133   $52.13   $52.15   $52.10  
  Purchase #6 $105.76   7.112%   $113.2817   $113.28   $113.30   $113.30  
  Purchase #7 $147.92   11.801%   $165.376   $165.38   $165.40   $165.40  
  7 purchase totals = $791.09       $863.4254   $863.42   $863.50   $863.50