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 $48.57   8.519%   $52.7077   $52.71   $52.70   $52.70  
  Purchase #2 $122.77   8.332%   $132.9992   $133.00   $133.00   $133.00  
  Purchase #3 $180.63   13.646%   $205.2788   $205.28   $205.30   $205.30  
  Purchase #4 $109.52   4.283%   $114.2107   $114.21   $114.20   $114.20  
  Purchase #5 $223.74   7.779%   $241.1447   $241.14   $241.15   $241.10  
  Purchase #6 $172.75   4.774%   $180.9971   $181.00   $181.00   $181.00  
  Purchase #7 $237.84   7.321%   $255.2523   $255.25   $255.25   $255.30  
  7 purchase totals = $1,095.82       $1,182.5905   $1,182.59   $1,182.60   $1,182.60