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 $204.83   9.502%   $224.2929   $224.29   $224.30   $224.30  
  Purchase #2 $121.55   8.711%   $132.1382   $132.14   $132.15   $132.10  
  Purchase #3 $22.27   7.570%   $23.9558   $23.96   $23.95   $24.00  
  Purchase #4 $117.33   6.103%   $124.4906   $124.49   $124.50   $124.50  
  Purchase #5 $177.97   6.491%   $189.522   $189.52   $189.50   $189.50  
  Purchase #6 $181.29   13.336%   $205.4668   $205.47   $205.45   $205.50  
  Purchase #7 $114.25   12.862%   $128.9448   $128.94   $128.95   $128.90  
  7 purchase totals = $939.49       $1,028.8111   $1,028.81   $1,028.80   $1,028.80