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 $169.84   9.619%   $186.1769   $186.18   $186.20   $186.20  
  Purchase #2 $145.63   11.398%   $162.2289   $162.23   $162.25   $162.20  
  Purchase #3 $174.70   5.346%   $184.0395   $184.04   $184.05   $184.00  
  Purchase #4 $170.62   11.641%   $190.4819   $190.48   $190.50   $190.50  
  Purchase #5 $123.94   9.716%   $135.982   $135.98   $136.00   $136.00  
  Purchase #6 $45.83   6.184%   $48.6641   $48.66   $48.65   $48.70  
  Purchase #7 $150.31   11.308%   $167.3071   $167.31   $167.30   $167.30  
  7 purchase totals = $980.87       $1,074.8804   $1,074.88   $1,074.95   $1,074.90