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 $194.67   11.232%   $216.5353   $216.54   $216.55   $216.50  
  Purchase #2 $94.74   12.501%   $106.5834   $106.58   $106.60   $106.60  
  Purchase #3 $180.66   11.486%   $201.4106   $201.41   $201.40   $201.40  
  Purchase #4 $33.61   9.349%   $36.7522   $36.75   $36.75   $36.80  
  Purchase #5 $247.85   9.408%   $271.1677   $271.17   $271.15   $271.20  
  Purchase #6 $20.26   6.305%   $21.5374   $21.54   $21.55   $21.50  
  Purchase #7 $48.80   9.835%   $53.5995   $53.60   $53.60   $53.60  
  7 purchase totals = $820.59       $907.5861   $907.59   $907.60   $907.60