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 $64.60   3.787%   $67.0464   $67.05   $67.05   $67.00  
  Purchase #2 $114.28   7.391%   $122.7264   $122.73   $122.75   $122.70  
  Purchase #3 $48.29   9.702%   $52.9751   $52.98   $53.00   $53.00  
  Purchase #4 $206.54   8.270%   $223.6209   $223.62   $223.60   $223.60  
  Purchase #5 $154.68   5.566%   $163.2895   $163.29   $163.30   $163.30  
  Purchase #6 $145.71   5.153%   $153.2184   $153.22   $153.20   $153.20  
  Purchase #7 $8.47   12.418%   $9.5218   $9.52   $9.50   $9.50  
  7 purchase totals = $742.57       $792.3985   $792.41   $792.40   $792.30