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 $156.92   8.281%   $169.9145   $169.91   $169.90   $169.90  
  Purchase #2 $96.76   5.469%   $102.0518   $102.05   $102.05   $102.10  
  Purchase #3 $177.90   13.321%   $201.5981   $201.60   $201.60   $201.60  
  Purchase #4 $23.55   3.140%   $24.2895   $24.29   $24.30   $24.30  
  Purchase #5 $167.91   13.591%   $190.7306   $190.73   $190.75   $190.70  
  Purchase #6 $80.41   5.119%   $84.5262   $84.53   $84.55   $84.50  
  Purchase #7 $41.30   4.506%   $43.161   $43.16   $43.15   $43.20  
  7 purchase totals = $744.75       $816.2717   $816.27   $816.30   $816.30