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 $60.94   10.645%   $67.4271   $67.43   $67.45   $67.40  
  Purchase #2 $196.42   4.270%   $204.8071   $204.81   $204.80   $204.80  
  Purchase #3 $230.66   6.446%   $245.5283   $245.53   $245.55   $245.50  
  Purchase #4 $130.29   8.428%   $141.2708   $141.27   $141.25   $141.30  
  Purchase #5 $73.96   10.109%   $81.4366   $81.44   $81.45   $81.40  
  Purchase #6 $245.81   4.740%   $257.4614   $257.46   $257.45   $257.50  
  Purchase #7 $152.34   9.601%   $166.9662   $166.97   $166.95   $167.00  
  7 purchase totals = $1,090.42       $1,164.8975   $1,164.91   $1,164.90   $1,164.90