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 $169.78   9.815%   $186.4439   $186.44   $186.45   $186.40  
  Purchase #2 $213.83   4.104%   $222.6056   $222.61   $222.60   $222.60  
  Purchase #3 $6.62   13.764%   $7.5312   $7.53   $7.55   $7.50  
  Purchase #4 $147.29   7.170%   $157.8507   $157.85   $157.85   $157.90  
  Purchase #5 $160.70   6.186%   $170.6409   $170.64   $170.65   $170.60  
  Purchase #6 $23.29   7.209%   $24.969   $24.97   $24.95   $25.00  
  Purchase #7 $209.55   10.588%   $231.7372   $231.74   $231.75   $231.70  
  7 purchase totals = $931.06       $1,001.7785   $1,001.78   $1,001.80   $1,001.70