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 $88.57   9.112%   $96.6405   $96.64   $96.65   $96.60  
  Purchase #2 $124.94   6.360%   $132.8862   $132.89   $132.90   $132.90  
  Purchase #3 $203.95   12.459%   $229.3601   $229.36   $229.35   $229.40  
  Purchase #4 $206.99   7.497%   $222.508   $222.51   $222.50   $222.50  
  Purchase #5 $168.45   9.526%   $184.4965   $184.50   $184.50   $184.50  
  Purchase #6 $229.92   9.385%   $251.498   $251.50   $251.50   $251.50  
  Purchase #7 $236.65   13.653%   $268.9598   $268.96   $268.95   $269.00  
  7 purchase totals = $1,259.47       $1,386.3491   $1,386.36   $1,386.35   $1,386.40