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 $220.29   12.491%   $247.8064   $247.81   $247.80   $247.80  
  Purchase #2 $81.61   4.152%   $84.9984   $85.00   $85.00   $85.00  
  Purchase #3 $232.87   12.726%   $262.505   $262.51   $262.50   $262.50  
  Purchase #4 $32.33   8.356%   $35.0315   $35.03   $35.05   $35.00  
  Purchase #5 $232.53   13.646%   $264.261   $264.26   $264.25   $264.30  
  Purchase #6 $182.42   11.582%   $203.5479   $203.55   $203.55   $203.50  
  Purchase #7 $244.39   11.421%   $272.3018   $272.30   $272.30   $272.30  
  7 purchase totals = $1,226.44       $1,370.4520   $1,370.46   $1,370.45   $1,370.40