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 $90.49   9.434%   $99.0268   $99.03   $99.05   $99.00  
  Purchase #2 $184.91   11.336%   $205.8714   $205.87   $205.85   $205.90  
  Purchase #3 $46.80   9.530%   $51.26   $51.26   $51.25   $51.30  
  Purchase #4 $234.57   7.205%   $251.4708   $251.47   $251.45   $251.50  
  Purchase #5 $116.88   10.810%   $129.5147   $129.51   $129.50   $129.50  
  Purchase #6 $168.65   9.504%   $184.6785   $184.68   $184.70   $184.70  
  Purchase #7 $61.93   3.367%   $64.0152   $64.02   $64.00   $64.00  
  7 purchase totals = $904.23       $985.8374   $985.84   $985.80   $985.90