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 $67.42   6.297%   $71.6654   $71.67   $71.65   $71.70  
  Purchase #2 $204.27   13.205%   $231.2439   $231.24   $231.25   $231.20  
  Purchase #3 $91.92   6.452%   $97.8507   $97.85   $97.85   $97.90  
  Purchase #4 $146.58   13.858%   $166.8931   $166.89   $166.90   $166.90  
  Purchase #5 $75.57   12.768%   $85.2188   $85.22   $85.20   $85.20  
  Purchase #6 $235.25   11.758%   $262.9107   $262.91   $262.90   $262.90  
  Purchase #7 $138.71   10.612%   $153.4299   $153.43   $153.45   $153.40  
  7 purchase totals = $959.72       $1,069.2125   $1,069.21   $1,069.20   $1,069.20