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 $59.76   12.668%   $67.3304   $67.33   $67.35   $67.30  
  Purchase #2 $184.55   11.371%   $205.5352   $205.54   $205.55   $205.50  
  Purchase #3 $5.93   5.133%   $6.2344   $6.23   $6.25   $6.20  
  Purchase #4 $109.43   9.754%   $120.1038   $120.10   $120.10   $120.10  
  Purchase #5 $176.89   10.715%   $195.8438   $195.84   $195.85   $195.80  
  Purchase #6 $232.43   10.870%   $257.6951   $257.70   $257.70   $257.70  
  Purchase #7 $157.35   8.335%   $170.4651   $170.47   $170.45   $170.50  
  7 purchase totals = $926.34       $1,023.2078   $1,023.21   $1,023.25   $1,023.10