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 $67.34   10.717%   $74.5568   $74.56   $74.55   $74.60  
  Purchase #2 $145.76   6.564%   $155.3277   $155.33   $155.35   $155.30  
  Purchase #3 $236.61   7.778%   $255.0135   $255.01   $255.00   $255.00  
  Purchase #4 $125.52   12.623%   $141.3644   $141.36   $141.35   $141.40  
  Purchase #5 $222.40   11.565%   $248.1206   $248.12   $248.10   $248.10  
  Purchase #6 $184.83   5.278%   $194.5853   $194.59   $194.60   $194.60  
  Purchase #7 $170.63   3.579%   $176.7368   $176.74   $176.75   $176.70  
  7 purchase totals = $1,153.09       $1,245.7051   $1,245.71   $1,245.70   $1,245.70