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 $170.67   3.309%   $176.3175   $176.32   $176.30   $176.30  
  Purchase #2 $173.29   9.667%   $190.0419   $190.04   $190.05   $190.00  
  Purchase #3 $183.50   7.667%   $197.5689   $197.57   $197.55   $197.60  
  Purchase #4 $122.33   8.621%   $132.8761   $132.88   $132.90   $132.90  
  Purchase #5 $98.94   4.605%   $103.4962   $103.50   $103.50   $103.50  
  Purchase #6 $241.29   9.385%   $263.9351   $263.94   $263.95   $263.90  
  Purchase #7 $186.43   5.410%   $196.5159   $196.52   $196.50   $196.50  
  7 purchase totals = $1,176.45       $1,260.7516   $1,260.77   $1,260.75   $1,260.70