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 $183.62   12.530%   $206.6276   $206.63   $206.65   $206.60  
  Purchase #2 $178.79   9.813%   $196.3347   $196.33   $196.35   $196.30  
  Purchase #3 $33.41   9.718%   $36.6568   $36.66   $36.65   $36.70  
  Purchase #4 $131.34   12.293%   $147.4856   $147.49   $147.50   $147.50  
  Purchase #5 $84.31   4.599%   $88.1874   $88.19   $88.20   $88.20  
  Purchase #6 $57.43   11.718%   $64.1596   $64.16   $64.15   $64.20  
  Purchase #7 $27.49   7.565%   $29.5696   $29.57   $29.55   $29.60  
  7 purchase totals = $696.39       $769.0213   $769.03   $769.05   $769.10