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 $65.88   5.527%   $69.5212   $69.52   $69.50   $69.50  
  Purchase #2 $244.91   8.820%   $266.5111   $266.51   $266.50   $266.50  
  Purchase #3 $170.58   6.760%   $182.1112   $182.11   $182.10   $182.10  
  Purchase #4 $219.33   5.284%   $230.9194   $230.92   $230.90   $230.90  
  Purchase #5 $222.36   8.581%   $241.4407   $241.44   $241.45   $241.40  
  Purchase #6 $13.58   5.243%   $14.292   $14.29   $14.30   $14.30  
  Purchase #7 $217.45   7.187%   $233.0781   $233.08   $233.10   $233.10  
  7 purchase totals = $1,154.09       $1,237.8737   $1,237.87   $1,237.85   $1,237.80