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 $158.62   5.682%   $167.6328   $167.63   $167.65   $167.60  
  Purchase #2 $247.78   11.261%   $275.6825   $275.68   $275.70   $275.70  
  Purchase #3 $149.76   4.636%   $156.7029   $156.70   $156.70   $156.70  
  Purchase #4 $225.37   13.403%   $255.5763   $255.58   $255.60   $255.60  
  Purchase #5 $184.80   4.869%   $193.7979   $193.80   $193.80   $193.80  
  Purchase #6 $205.50   6.545%   $218.95   $218.95   $218.95   $219.00  
  Purchase #7 $143.61   6.288%   $152.6402   $152.64   $152.65   $152.60  
  7 purchase totals = $1,315.44       $1,420.9826   $1,420.98   $1,421.05   $1,421.00