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 $161.69   13.514%   $183.5408   $183.54   $183.55   $183.50  
  Purchase #2 $226.69   13.280%   $256.7944   $256.79   $256.80   $256.80  
  Purchase #3 $60.67   6.709%   $64.7404   $64.74   $64.75   $64.70  
  Purchase #4 $133.83   9.400%   $146.41   $146.41   $146.40   $146.40  
  Purchase #5 $120.87   8.493%   $131.1355   $131.14   $131.15   $131.10  
  Purchase #6 $187.60   13.819%   $213.5244   $213.52   $213.50   $213.50  
  Purchase #7 $205.27   6.425%   $218.4586   $218.46   $218.45   $218.50  
  7 purchase totals = $1,096.62       $1,214.6041   $1,214.60   $1,214.60   $1,214.50