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 $164.49   6.149%   $174.6045   $174.60   $174.60   $174.60  
  Purchase #2 $189.47   8.508%   $205.5901   $205.59   $205.60   $205.60  
  Purchase #3 $64.99   13.741%   $73.9203   $73.92   $73.90   $73.90  
  Purchase #4 $204.70   8.698%   $222.5048   $222.50   $222.50   $222.50  
  Purchase #5 $63.46   11.764%   $70.9254   $70.93   $70.95   $70.90  
  Purchase #6 $200.87   13.367%   $227.7203   $227.72   $227.70   $227.70  
  Purchase #7 $59.78   13.801%   $68.0302   $68.03   $68.05   $68.00  
  7 purchase totals = $947.76       $1,043.2956   $1,043.29   $1,043.30   $1,043.20