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 $169.81   10.874%   $188.2751   $188.28   $188.30   $188.30  
  Purchase #2 $163.99   9.549%   $179.6494   $179.65   $179.65   $179.60  
  Purchase #3 $160.57   13.336%   $181.9836   $181.98   $182.00   $182.00  
  Purchase #4 $184.93   13.228%   $209.3925   $209.39   $209.40   $209.40  
  Purchase #5 $108.68   7.836%   $117.1962   $117.20   $117.20   $117.20  
  Purchase #6 $185.35   7.798%   $199.8036   $199.80   $199.80   $199.80  
  Purchase #7 $172.79   8.173%   $186.9121   $186.91   $186.90   $186.90  
  7 purchase totals = $1,146.12       $1,263.2125   $1,263.21   $1,263.25   $1,263.20