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 $93.70   3.691%   $97.1585   $97.16   $97.15   $97.20  
  Purchase #2 $116.68   13.701%   $132.6663   $132.67   $132.65   $132.70  
  Purchase #3 $59.47   10.817%   $65.9029   $65.90   $65.90   $65.90  
  Purchase #4 $220.55   11.762%   $246.4911   $246.49   $246.50   $246.50  
  Purchase #5 $86.56   10.472%   $95.6246   $95.62   $95.60   $95.60  
  Purchase #6 $153.58   6.449%   $163.4844   $163.48   $163.50   $163.50  
  Purchase #7 $189.28   5.239%   $199.1964   $199.20   $199.20   $199.20  
  7 purchase totals = $919.82       $1,000.5242   $1,000.52   $1,000.50   $1,000.60