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 $134.83   8.419%   $146.1813   $146.18   $146.20   $146.20  
  Purchase #2 $201.46   5.659%   $212.8606   $212.86   $212.85   $212.90  
  Purchase #3 $70.74   3.611%   $73.2944   $73.29   $73.30   $73.30  
  Purchase #4 $22.99   6.589%   $24.5048   $24.50   $24.50   $24.50  
  Purchase #5 $62.57   7.697%   $67.386   $67.39   $67.40   $67.40  
  Purchase #6 $186.77   9.749%   $204.9782   $204.98   $205.00   $205.00  
  Purchase #7 $160.39   7.599%   $172.578   $172.58   $172.60   $172.60  
  7 purchase totals = $839.75       $901.7833   $901.78   $901.85   $901.90